Synthesis of [3,5,7]-H-imidazo[1,5-a] imidazol-2(3H)-one compounds

ABSTRACT

Individual substituted [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds and their pharmaceutically-acceptable salts are disclosed, as are libraries of such compounds. Methods of preparing and using the libraries of compounds as well as individual compounds of the libraries are also disclosed.

This a continuation-in-part of application Ser. No. 60/154,443, filed Sep. 17, 1999, whose disclosures are incorporated herein by reference.

DESCRIPTION

1. Technical Field

The present invention relates generally to the combinatorial synthesis of [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one derivatives. More specifically, the invention provides novel [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds as well as novel combinatorial libraries comprised of many such compounds, and methods of synthesizing the libraries.

2. Background Information

The process of discovering new therapeutically active compounds for a given indication involves the screening of all compounds from available compound collections. From the compounds tested one or more structure(s) is selected as a promising lead. A large number of related analogs are then synthesized to develop a structure-activity relation-ship and select one or more optimal compounds. With traditional one-at-a-time synthesis and biological testing of analogs, this optimization process is long and labor intensive.

Adding significant numbers of new structures to the compound collections used in the initial screening step of the discovery and optimization process cannot be accomplished with traditional one-at-a-time synthesis methods, except over a time frame of months or even years. Faster methods are needed that permit the preparation of up to thousands of related compounds in a matter of days or a few weeks. This need is particularly evident when it comes to synthesizing more complex compounds, such as the [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds of the present invention.

Solid-phase techniques for the synthesis of peptides have been extensively developed and combinatorial libraries of peptides have been prepared with great success. During the past four years there has been substantial development of chemically synthesized combinatorial libraries (SCLs) made up of peptides.

The preparation and use of synthetic peptide combinatorial libraries has been described for example by Dooley in U.S. Pat. No. 5367.053; Huebner in U.S. Pat. No. 5,182,366; Appel et al in WO Pct 92/09300; Geysen in published European Patent Application 0 138 855 and Pimmg in U.S. Pat. No. 5,143,854. Such SCLs provide the efficient synthesis of an extraordinary number of various peptides in such libraries and the rapid screening of the library that identifies lead pharmaceutical peptides.

Peptides have been, and remain, attractive targets for drug discovery. Their high affinities and specificities toward biological receptors as well as the ease with which large peptide libraries can be combinatorially synthesized make them attractive drug targets. The screening of peptide libraries has led to the identification of many biologically-active lead compounds. However, the therapeutic application of peptides is limited by their poor stability and bioavailability in vivo. Therefore, there is a need to synthesize and screen compounds that can maintain high affinity and specificity toward biological receptors, while exhibiting improved pharmacological properties relative to peptides.

Combinatorial approaches have recently been extended to “organic” or non-peptide libraries.

Significantly, many biologically active compounds contain the imidazole moiety. Such compounds are conformationally constrained scaffolds, are quite common in nature and many imidazole-containing natural products have been isolated encompassing a wide range of biological activities. The imidazole ring system is of particular importance because it is present in the essential amino acid histidine. The histidine residues are found at the active site of ribonuclease and several other enzymes. Drugs such as cimetidine were designed with histamine itself as the starting point [C. R. Ganellin, in Medicinal Chemistry, ed. S. M. Roberts and B. J. Price, Academic Press, London, 1985, p.93; G. J. Durant, Chem Soc. Rev., 1985, 84, 375].

Several other classes of drugs are based on the imidazole ring. 2-Nitroimidazole (azomycin) is a naturally occurring antibiotic and some synthetic nitroimidazoles are active against intestinal infections (Reviews: Nitroimidazoles; Chemistry; Pharmacology and Clinical Applications, eds. A. Breccia, B. Cavalleri, and G. E. Adams, Plenum Press, New York, 1982; J. H. Boyer, Nitrazoles, VCH, Deerfield Beach, Fla., 1986).

Imidazole-containing moieties are found in many biologically active compounds and are known to have useful therapeutic implications. There is a need to further study and develop large numbers of [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds and their binding to biological receptors. These compounds of the present invention are principally derived from the synthesis of dipeptides, but the dipeptides are substantially modified. In short, they are chemically modified through, acylation and cyclization via Bischler-Naprielski reaction into the subject [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one, thus providing mixtures and individual compounds of substantial diversity.

BRIEF SUMMARY OF THE INVENTION

The invention provides a rapid approach for combinatorial synthesis and screening of individual compounds and libraries of [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds. The present invention further provides libraries and individual compounds and their pharmaceutically-acceptable salts of Formula I. The present invention also relates to the preparation of synthetic combinatorial libraries of organic compounds and their pharmaceutically-acceptable salts of Formula I, wherein R¹, R² and R³ have the meanings provided below.

The present invention has several benefits and advantages. One benefit is the provision of a new synthesis for bicyclic [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds. The present invention provides a large array of diverse [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds that can be screened for biological activity, and as described below, are biologically active.

An advantage of the invention is that individual compounds can be prepared or libraries containing a plurality of compounds can be prepared.

Another benefit of the invention is that the yield of bicyclic compound produced is relatively great compared to that obtained in prior syntheses of the parental compound.

Still further benefits and advantages of the invention will be apparent to the skilled worker from the discussion that follows.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the preparation and use of synthetic combinatorial libraries and individual compounds of a [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one also referred to as a imidazo-imidizol-one that correspond in structure to Formula I, and their pharmaceutically-acceptable salts:

wherein:

R¹ and R² are independently selected from the group consisting of a hydrogen atom (hydrido), C₁-C₁₀ alkyl, C₁-C₁₀ substituted alkyl, C₇-C₁₆ phenylalkyl, C₇-C₁₆ substituted phenylalkyl, phenyl, substituted phenyl, C₃-C₇ cycloalkyl, and a C₃-C₇ substituted cycloalkyl group.

R³ is selected from the group consisting of a hydrido, C₁-C₁₀ alkyl, C₁-C₁₀ substituted alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ substituted alkenyl, C₂-C₁₀ alkynyl, C₂-C₁₀ substituted alkynyl, C₃-C₇ substituted cycloalkyl, phenyl, C₇-C₁₆ phenylalkyl, C₇-C₁₆ phenylalkenyl, C₇-C₁₆ phenylalkenyl and a C₇-C₁₆ substituted phenylalkenyl group.

In one embodiment of the above bicyclic imidazo-imidizol-one of Formula I, wherein

R¹ and R² are independently selected from the group consisting of a hydrido, methyl, benzyl, 2-butyl, aminobutyl, N,N-dimethylaminobutyl, N-methylaminobutyl, N-methyl-N-benzylaminobutyl, 2-methylpropyl, methylsulfinylethyl, methylthioethyl, N,N-dimethylaminoethyl,N,N-dimethyl-aminopropyl, N,N,N-trimethylguanidinopropyl, N,N,N-tribenzylguanidinopropyl,N,N-dibenzylguanidinopropyl, N-methylguanidinopropyl, hydroxymethyl, 1-hydroxyethyl, 2-propyl, N-methyl-3-indolylmethyl, 4-methoxybenzyl, 4-hydroxybenzyl, propyl, butyl, cyclohexylmethyl, phenyl, 2-naphthylmethyl, and a 4-imidazolylmethyl substituent; and

R³ is selected from the group consisting of a 1-phenyl-1-cyclopropyl, 1-phenylbutyl, 2-phenylbutyl, 3-fluorobenzyl, 3-bromobenzyl, α,α,α-trifluoro-m-xylyl, p-xylyl, 4-fluorobenzyl, 3-methoxybenzyl, 4-bromobenzyl, 4-methoxybenzyl, 4-ethoxybenzyl, 4-isobutyl-α-methyl-benzyl, 3,4-dichlorobenzyl, 3,5-bis-(trifluoromethyl)-benzyl, 2-(3,4-dimethoxyphenyl)-ethyl, 4-biphenylmethyl, β-methylstyryl, 2-(trifluoromethyl)-styryl, 3,4-dimethoxybenzyl, 3,4-dihydroxybenzyl, 2-methoxystyryl, 3,4-dihydroxystyryl, 2-hydroxystyryl, phenyl, 4-chlorostyryl, 3-methoxyphenyl, 4-isopropylphenyl, 4-vinylphenyl, 4-fluorophenyl, 4-bromophenyl, 3,4-dimethoxystyryl, 4-hydroxyphenyl, trans-styryl, 3,4-dimethylphenyl, 3-fluoro-4-methylphenyl, 3-bromo-4-methyl-phenyl, 3-iodo-4-methyl-phenyl, 3,4-dichlorophenyl, 4-biphenyl, 3,4-difluorophenyl, m-tolyl, benzyl, phenethyl, 3-methoxy-4-methylphenyl, 3-phenylpropyl, 4-butylphenyl, 3,5-dimethylphenyl, 3,5-bis-(trifluoromethyl)-phenyl, 3,4-dimethoxyphenyl, 4-ethyl-4-biphenyl, 3,4,5-triethoxyphenyl, propyl, hexyl, isopropyl, 2-butyl, isobutyl, 2-pentyl, isovaleryl, 3-heptyl, 1-propenyl, 2-propenyl, trans-2-pentenyl, 1-ethyl-1-pentenyl, p-tolyl, p-anisyl, t-butyl, neopentyl, cyclohexyl, cyclohexylmethyl, dicyclohexylmethyl, cyclohexylpropyl, cycloheptyl, methyl, 2-methylcyclopropyl, cyclobutyl, cyclopentyl, cyclopentylethyl, 2-furyl, cyclohexylethyl, 4-methylcyclohexyl, 4-tert-butyl-cyclohexyl, 1-adamantyl, 4-methylcyclohexylmethyl, 1,3-pentadienyl, 2-buten-2-yl, 2-norbornanemethyl, 1-adamantanemethyl, and a 3-pentyl, 2-thiophene substituent.

In one of the preferred embodiments of the present invention, the R groups are those as immediately defined above.

In the above Formula the stereochemistry of he chiral R¹ group can independently be in the R or S onfiguration, or a mixture of the two. For instance, as will be described in further detail below, the R¹ group can be the side chain substituent of the α-carbon of various amino acids. The amino acids can be in the L- or D-configuration, resulting in the same R group varying only in its stereochemistry. As a consequence of an R¹ substituent being in one or both or two stereoconfigurations, the R¹ group is usually illustrated bonded to the bicyclic ring by a wavy line.

It is also noted that a compound of Formula I can exist in two tautomeric forms; i.e., in the keto or enol forms. Those two tautomeric forms are illustrated in Formula IA, below.

For convenience, a contemplated compound of Formula I (IA) is usually depicted and discussed as being in the keto form (imidazo-imidizol-one) with the understanding that both keto and enol forms are present in equilibrium.

Formulas of the two tautomers in both stereoconfigurations are shown below.

In any of the Formulas herein, the term “C₁-C₁₀ alkyl” denotes a straight or branched chain radical such as a methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, amyl, tert-amyl, hexyl, heptyl, decyl group and the like. The term “lower alkyl” denotes a C₁-C₄ alkyl group. A preferred “C₁-C₁₀ alkyl” group is a methyl group.

The term “C₂-C₁₀ alkenyl” denotes a radical such as a vinyl, allyl, 2-butenyl, 3-butenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, 2-heptenyl, 3-heptenyl, 4-heptenyl, 5-heptenyl, 6-heptenyl and a 2-decenyl group and the like, as well as dienes and trienes of straight and branched chains containing up to ten carbon atoms and at least one carbon-to-carbon (ethylenic) double bond.

The term “C₂-C₁₀ alkynyl” denotes a radical such as ethynyl, propynyl, butynyl, pentynyl, hexynyl, heptynyl, decynyl and the like, as well as di- and triynes of straight and branched chains containing up to ten carbon atoms and at least one carbon-to-carbon (acetylenic) triple bond.

The term “C₁-C₁₀ substituted alkyl”, “C₂-C₁₀ substituted alkenyl” and “C₂-C₁₀ substituted alkenyl” denote that the above C₁-C₁₀ alkyl group and C₂-C₁₀ alkenyl and alkynyl groups are substituted by one or more, and preferably one or two, halogen, hydroxy, protected hydroxy, C₃-C₇ cycloalkyl, C₃-C₇ substituted cycloalkyl, naphthyl, substituted naphthyl, adamantyl, abietyl, thiofuranyl, indolyl, substituted indolyl, amino, protected amino, (monosubstituted)amino, protected (monosubstituted) amino, (disubstituted) amino, guanidino, (monosubstituted)guanidino, (disubstituted)guanidino, (trisubstituted)guanidino, imidazolyl pyrolidinyl, C₁-C₇ acyloxy, nitro, heterocycle, substituted heterocycle, C₁-C₄ alkyl ester, carboxy, protected carboxy, carbamoyl, carbamoyloxy, carboxamide, protected carboxamide, cyano, methylsulfonylamino, methylsulfonyl, sulfhydryl, C₁-C₄ alkylthio, C₁-C₄ alkyl sulfonyl or C₁-C₄ alkoxy groups. The substituted alkyl groups can be substituted once or more, and preferably once or twice, with the same or with different substituents.

Examples of the above substituted alkyl groups include the cyanomethyl, nitromethyl, chloromethyl, hydroxymethyl, tetrahydro-pyranyloxymethyl, trityloxymethyl, propionyloxymethyl, aminomethyl, carboxymethyl, allyloxycarbonylmethyl, allylcarbonyl-aminomethyl, carbamoyloxymethyl, methoxymethyl, ethoxymethyl, t-butoxymethyl, acetoxymethyl, chloromethyl, bromomethyl, iodomethyl, 6-hydroxy-hexyl, 2,4-dichloro(n-butyl), 2-amino(isopropyl), 2-carbamoyloxyethyl chloroethyl, bromoethyl, fluoroethyl, iodoethyl, chloropropyl, bromopropyl, fluoropropyl, iodopropyl and the like.

In preferred embodiments of the subject invention, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₁-C₁₀ substituted alkyl, C₂-C₁₀ substituted alkenyl, or C₂-C₁₀ substituted alkynyl, are more preferably C₁-C₇ or C₂-C₇, respectively, and more preferably, C₁-C₆ or C₂-C₆ as is appropriate for unsaturated substituents. However, it should be appreciated by those of skill in the art that one or a few carbons usually can be added to an alkyl, alkenyl, alkynyl, substituted or unsubstituted, without substantially modifying the structure and function of the subject compounds and that, therefore, such additions would not depart from the spirit of the invention.

The term “C₁-C₄ alkoxy” as used herein denotes groups that are ether groups containing up to four carbon atoms such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, t-butoxy and like groups. A preferred C₁-C₄ alkoxy group is methoxy.

The term “C₁-C₇ acyloxy” denotes a carboxy group-containing substituent containing up seven carbon atoms such as formyloxy, acetoxy, propanoyloxy, butanoyloxy, pentanoyloxy, hexanoyloxy, heptanoyloxy, benzoyloxy and the like.

Similarly, the term “C₁-C₇ acyl” encompasses groups such as formyl, acetyl, propionoyl, butyroyl, pentanoyl, hexanoyl, heptanoyl, benzoyl and the like.

The substituent term “C₃-C₇ cycloalkyl” includes the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl rings. The substituent term “C₃-C₇ substituted cycloalkyl” indicates an above cycloalkyl ring substituted by a halogen, hydroxy, protected hydroxy, phenyl, substituted phenyl, heterocycle, substituted heterocycle, C₁-C₁₀ alkyl, C₁-C₄ alkoxy, carboxy, protected carboxy, amino, or protected amino.

The substituent term “C₅-C₇ cycloalkenyl” indicates a substituent that is itself a 1-, 2-, or 3-substituted cyclopentenyl ring, a 1-, 2- , 3- or 4-substituted cyclohexenyl ring or a 1-, 2-, 3-,4- or 5-substituted cycloheptenyl ring, whereas the term “substituted C₃-C₇ cycloalkenyl” denotes the above C₃-C₇ cycloalkenyl rings substituted by a C₁-C₁₀ alkyl radical, halogen, hydroxy, protected hydroxy, C₁-C₄ alkoxy, carboxy, protected carboxy, amino, or protected amino,

The term “heterocyclic ring” or “heterocycle” denotes an optionally substituted 5-membered or 6-membered ring that has 1 to 4 heteroatoms, such as oxygen, sulfur and/or nitrogen, in particular nitrogen either alone or in conjunction with sulfur or oxygen ring atoms. These five-membered or six-membered rings can be fully unsaturated or partially unsaturated, with fully unsaturated rings being preferred.

Preferred heterocyclic rings include pyridino, pyrimidino, and pyrazino, furano, and thiofurano rings. The heterocyles can be substituted or unsubstituted as for example, with such substituents as those described in relation to substituted phenyl or substituted naphthyl.

The term “C₇-C₁₆ phenylalkyl” or “C₇-C₁₆ aralkyl” denotes a C₁-C₁₀ alkyl group substituted at any position by a phenyl ring. Examples of such a group include benzyl, 2-phenylethyl, 3-phenyl(n-prop-1-yl), 4-phenyl(hex-1-yl), 3-phenyl(n-am-2-yl), 3-phenyl(sec-butyl), and the like. A preferred C₇-C₁₆ phenylalkyl group is the benzyl group.

The term “C₇-C₁₆ substituted phenylalkyl” denotes an above C₇-C₁₆ phenylalkyl group substituted on the C₁-C₁₀ alkyl portion with one or more, and preferably one or two, groups selected from the group consisting of a halogen, hydroxy, protected hydroxy, keto, C₂-C₃ cyclic ketal phenyl, amino, protected amino, C₁-C₇ acyloxy, nitro, carboxy, protected carboxy, carbamoyl, carbamoyloxy, cyano, N-(methyl-sulfonylamino) or C₁-C₄ alkoxy group, whose phenyl group portion can be substituted with 1 or 2 groups selected from the group consisting of a halogen, hydroxy, protected hydroxy, nitro, C₁-C₁₀ alkyl, C₁-C₆ substituted alkyl, C₁-C₄ alkoxy, carboxy, protected carboxy, carboxymethyl, protected carboxymethyl, hydroxymethyl, protected hydroxymethyl, aminomethyl, protected aminomethyl, amino, (monosubstituted)amino, (disubstituted)amino, a N-(methylsulfonylamino) group, or a phenyl group that is itself substituted or unsubstituted. When either the C₁-C₁₀ alkyl portion or the phenyl portion or both are mono- or di-substituted, the substituents can be the same or different.

Examples of “C₇-C₁₆ substituted phenylalkyl” include groups such as 2-phenyl-1-chloroethyl, 2-(4-methoxyphenyl)eth-1-yl, 2,6-dihydroxy-4-phenyl(n-hex-2-yl), 5-cyano-3-methoxy-2-phenyl(n-pent-3-yl), 3-(2,6-dimethylphenyl)n-prop-1-yl, 4-chloro-3-aminobenzyl, 6-(4-methoxyphenyl)-3-carboxy(n-hex-1-yl), 5-(4-aminomethyl-phenyl)-3-(aminomethyl)(n-pent-2-yl), 5-phenyl-3-keto-(n-pent-1-yl), 4-(4-aminophenyl)-4-(I.4-oxetanyl)(n-but-1-yl), and the like.

The term “C₇-C₁₆ phenylalkenyl” denotes a C₁-C₁₀ alkenyl group substituted at any position by a phenyl ring. The term “C₇-C₁₆ substituted phenylalkenyl” denotes a C₇-C₁₆ arylalkenyl group substituted on the C₁-C₁₀ alkenyl portion. Substituents can the same as those as defined above in relation to C₇-C₁₆ phenylalkyl and C₇-C₁₆ substituted phenylalkyl. A preferred C₇-C₁₆ substituted phenylalkenyl is 3-(4-nitrophenyl)-2-propenyl.

The term “substituted phenyl” specifies a phenyl group substituted at one or more positions, preferably at one or two positions, with moieties selected from the group consisting of halogen, hydroxy, protected hydroxy, cyano, nitro, C₁-C₁₀ alkyl, C₁-C₁₀ substituted alkyl, C₁-C₄ alkoxy, carboxy, protected carboxy, carboxymethyl, protected carboxymethyl, hydroxymethyl, protected hydroxymethyl, amino, protected anilino, (monosubstituted)amino, protected (monosubstituted) amino, (disubstituted)amino, trifluoromethyl, N-(methylsulfonylamino), or phenyl that is itself substituted or unsubstituted such that, for example, a biphenyl group results.

Illustrative substituents embraced by the term “substituted phenyl” include a mono- or di(halo)phenyl group such as 4-chlorophenyl, 2,6-dichlorophenyl, 2,5-dichlorophenyl, 3,4-dichlorophenyl, 3-chlorophenyl, 3-bromophenyl, 4-bromophenyl, 3,4-dibromophenyl, 3-chloro-4-fluorophenyl, 2-fluorophenyl and the like; a mono or di(hydroxy)phenyl groups such as 4-hydroxyphenyl, 3-hydroxyphenyl, 2,4-dihydroxyphenyl, the protected hydroxy derivatives thereof and the like; a nitrophenyl group such as 3- or 4-nitrophenyl, a cyanophenyl group for example, 4-cyanophenyl; a mono-or di(lower alkyl)phenyl group such as 4-methylphenyl, 2,4-dimethylphenyl, 2-methylphenyl, 4-(isopropyl)phenyl, 4-ethylphenyl, 3-(n-prop-1-yl)phenyl and the like: a mono or di(alkoxyl)phenyl group for example, 2,6-dimethoxyphenyl, 4-methoxyphenyl, 3-ethoxyphenyl, 4-(isopropoxy)phenyl, 4-(t-butoxy)-phenyl, 3-ethoxy-4-methoxyphenyl, 3-(4-methyl phenoxy)phenyl, and the like; 3- or 4-trifluoromethylphenyl; a mono- or dicarboxyphenyl or (protected carboxy)phenyl group such as 4-carboxyphenyl or 2,4-di(protected carboxy)phenyl; a mono-or di(hydroxymethyl)phenyl or (protected hydroxymethyl)phenyl such as 3-(protected hydroxymethyl)phenyl or 3,4-di(hydroxymethyl)phenyl; a mono- or di(aminomethyl) phenyl or (protected aminomethyl)phenyl such as 2-(aminomethyl)phenyl or 2,4-(protected aminomethyl) phenyl; or a mono- or di(N-(methylsulfonylamino))phenyl such as 3-(N-(methylsulfonylamino))phenyl. Also, the term “substituted phenyl” represents disubstituted phenyl groups wherein the substituents are different. For example, 3-methyl-4-hydroxyphenyl, 3-chloro-4-hydroxyphenyl, 2-methoxy-4-bromophenyl, 4-ethyl-2-hydroxyphenyl, 3-hydroxy-4-nitrophenyl, 2-hydroxy-4-chlorophenyl and the like are contemplated.

The term “substituted naphthyl” specifies a naphthyl group substituted with one or more, and preferably one or two moieties selected from the group consisting of a halogen, hydroxy, protected hydroxy, cyano, nitro, C₁-C₁₀ alkyl, C₁-C₄ alkoxy, carboxy, protected carboxy, carboxymethyl, protected carboxymethyl, hydroxymethyl, protected hydroxymethyl, amino, protected amino, (monosubstituted) amino, protected (monosubstituted)amino, (disubstituted) amino trifluoromethyl, or a N-(methylsulfonylamino) group. Examples of substituted naphthyl include 2-(methoxy)naphthyl and 4-(methoxy)naphthyl.

The term “substituted indolyl” specifies a indolyl group substituted, either at the nitrogen or carbon, or both, with one or more, and preferably one or two, moieties selected from the group consisting of a halogen, hydroxy, protected hydroxy, cyano, nitro, C₁-C₁₀ alkyl, C₁-C₁₀ substituted alkyl, C₁-C₁₀ alkenyl, C₇-C₁₆ phenylalkyl, C₇-C₁₆ substituted phenylalkyl, C₁-C₆ alkoxy, carboxy, protected carboxy, carboxymethyl, protected carboxymethyl, hydroxymethyl, protected hydroxymethyl, amino, protected amino, monosubstituted amino, or a disubstituted amino group.

Examples of the term “substituted indolyl” includes such groups as 6-fluoro, 5-fluoro, 5-bromo, 5-hydroxy, 5-methyl, 6-methyl, 7-methyl, 1-methyl, 1-ethyl, 1-benzyl, 1-napthylmethyl, and the like. An example of a disubstituted indolyl is 1-methyl-5-methyl indolyl.

The terms “halo” and “halogen” refer to the fluoro, chloro, bromo, or iodo groups.

The term “(monosubstituted)amino” refers to an amino group with one substituent selected from the group consisting of phenyl, substituted phenyl, C₁-C₁₀ alkyl, and C₇-C₁₆ arylalkyl, wherein the latter three substituent terms are as defined above. The (monosubstituted)amino can additionally have an amino-protecting group as encompassed by the term “protected (monosubstituted)amino.”

The term “(disubstituted)amino” refers to amino groups with two substituents selected from the group consisting of phenyl, substituted phenyl, C₁-C₁₀ alkyl, and C₇-C₁₆ arylalkyl wherein the latter three substituent terms are as described above. The two substituents can be the same or different.

The terms “(monosubstituted)guanidino”, “(disubstituted)guanidino.” and “(trisubstituted)-guanidino” are used to mean that a guanidino group is substituted with one, two, or three substituents, respectively. The substituents can be any of those as defined above in relation to (monosubstituted)-amino and (disubstituted)amino and, where more than one substituent is present, the substituents can be the same or different.

The terms “(monosubstituted) imidizol-one imidazole, “(disubstituted) imidizol-one imidazole.” and “(trisubstituted) imidizol-one imidazole” mean compounds in which the imidizol-one imidazole group is substituted with one, two, or three substituents, respectively. The substituents can be any of those as defined above in relation to a (monosubstituted)-amino or (disubstituted)amino group and where more than one substituent is present. The substituents can be the same or different.

The term “amino-protecting group” as used herein refers to one or more selectively removable substituents on the amino group commonly employed to block or protect the amino functionality. The term “protected (monosubstituted)amino” means there is an amino-protecting group on the monosubstituted amino nitrogen atom. In addition, the term “protected carboxamide” means there is an amino-protecting group present replacing the proton of the amido nitrogen so that di-N-alkylation.

Examples of such amino-protecting groups include the formyl (“For”) group, the trityl group (Trt), the phthalimido group, the trichloroacetyl group, the chloroacetyl, bromoacetyl, and iodoacetyl groups. Urethane blocking groups, such as t-butoxycarbonyl (“Boc”), 2-(4-biphenylyl)propyl(2)-oxycarbonyl (“Bpoc”), 2-phenylpropyl(2)oxycarbonyl (“Poc”), 2-(4-xenyl)-isopropoxycarbonyl, 1,1-diphenylethyl(1)oxycarbonyl, 1,1-diphenylpropyl(1)oxycarbonyl, 2-(3,5-dimethoxyphenyl) propyl(2)oxycarbonyl (“Ddz”), 2-(p-5-toluyl)propyl(2)oxycarbonyl, cyclo-pentanyloxycarbonyl, 1-methylcyclopentanyl-oxycarbonyl, cyclohexanyloxycarbonyl, 1-methylcyclohexanyloxycarbonyl, 2-methylcyclohexanyloxycarbonyl, 2-(4-toluylsulfonyl)ethoxycarbonyl, 2-(methylsulfonyl)ethoxycarbonyl, 2-(triphenylphosphino)ethoxycarbonyl, 9-fluoroenylmethoxycarbonyl (“Fmoc”), 2-(trimethylsilyl)ethoxycarbonyl, allyloxycarbonyl, 1-(trimethylsilylmethyl)prop-1-enyloxycarbonyl, 5-benz-isoxalylmethoxycarbonyl, 4-acetoxybenzyloxycarbonyl, 2,2,2-trichloroethoxycarbonyl, 2-ethynyl(2)propoxycarbonyl, cyclopropylmethoxycarbonyl, isobornyloxycarbonyl, 1-piperidyloxycarbonyl, benzyloxycarbonyl (“Z”), 4-phenylbenzyloxycarbonyl, 2-methylbenzyloxycarbonyl, α-2,4,5,-tetramethylbenzyloxycarbonyl (“Tmz”), 4-methoxybenzyl-oxycarbonyl, 4-fluorobenzyloxycarbonyl, 4-chloro-benzyloxycarbonyl, 3-chlorobenzyloxycarbonyl, 2-chlorobenzyloxycarbonyl, dichlorobenzyloxycarbonyl, 4-bromobenzyloxycarbonyl, 3-bromobenzyloxycarbonyl, 4-nitrobenzyloxycarbonyl, 4-cyanobenzyioxycarbonyl, 4-(decyloxy)benzyloxycarbonyl, and the like, the benzoylmethylsulfonyl group, dithiasuccinoyl (“Dts”) group, the 2-(nitro)phenylsulfenyl group (“Nps”), the diphenylphosphine oxide group, and like amino-protecting groups. The species of amino-protecting group employed is usually not critical so long as the derivatized amino group is stable to the conditions of the subsequent reactions and can be removed at the appropriate point without disrupting the remainder of the compound. Preferred amino-protecting groups are Boc and Fmoc.

Further examples of amino-protecting groups embraced to by the above term are well known in organic synthesis and the peptide art and are described by, for example T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2^(nd) ed., John Wiley and Sons. New York., Chapter 7, 1991; M. Bodanzsky, Principles of Peptide Synthesis, 1^(st) and 2^(nd) revised eds., Springer-Verlag, New York, 1984 and 1993; and Stewart and Young, Solid Phase Peptide Synthesis, 2^(nd) ed., Pierce Chemical Co, Rockford. Ill. 1984.

The related term “protected amino” defines an amino group substituted with an amino-protecting group discussed above.

The term “carboxy-protecting group” as used herein refers to one of the ester derivatives of the carboxylic acid group commonly employed to block or protect the carboxylic acid group while reactions are carried out on other functional groups on the compound. Examples of such carboxylic acid protecting groups include 4-nitrobenzyl, 4-methoxybenzyl, 3,4-dimethoxybenzyl, 2,4-dimethoxybenzyl, 2,4,6-trimethoxybenzyl, 2,4,6-trimethylbenzyl, pentamethylbenzyl, 3,4-methylene-dioxybenzyl, benzhydryl, 4,4′-methoxytrityl, 4,4′,4″-trimethoxytrityl, 2-phenylprop-2-yl, trimethylsilyl, t-butyldimethylsilyl, 2,2,2-trichloroethyl, β-(trimethylsilyl)ethyl, β-[di(n-butyl)-methylsilyl]ethyl, β-toluenesulfonylethyl, 4-nitrobenzyl-sulfonylethyl, allyl, cinnamyl, 1-(trimethylsilylmethyl)-prop-1-en-3-yl, and like moieties. The species of carboxy-protecting group employed is also usually not critical so long as the derivatized carboxylic acid is stable to the conditions of subsequent reactions and can be removed at the appropriate point without disrupting the remainder of the molecule.

Further examples of these groups are found in E. Haslam, Protective Groups in Organic Chemistry, J. G. W. McOmie Ed., Plenum Press, New York 1973, Chapter 5 and T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis 2^(nd) ed., John Wiley and Sons, New York, 1991, Chapter 5, each of which is incorporated herein by reference. A related term is “protected-carboxy”, which refers to a carboxy group substituted with one of the above carboxy-protecting groups.

The term “hydroxy-protecting group” refers to readily cleavable groups bonded to hydroxyl groups, such as the tetrahydropyranyl, 2-methoxyprop-2-yl, 1-ethoxyeth-1-yl, methoxymethyl, β-methoxyethoxymethyl, methylthiomethyl, t-butyl, t-amyl, trityl, 4-methoxytrityl, 4,4′-dimethoxytrityl, 4,4′,4″-trimethoxytrityl, benzyl, allyl, trimethylsilyl, (t-butyl)dimethylsilyl and 2,2,2-trichloroethoxycarbonyl groups, and the like. The species of hydroxy-protecting groups is also usually not critical so long as the derivatized hydroxyl group is stable to the conditions of subsequent reaction(s) and can be removed at the appropriate point without disrupting the remainder of the compound.

Further examples of hydroxy-protecting groups are described by C. B. Reese and E Haslam, Protective Groups in Organic Chemistry, J. G. W. McOmie, Ed., Plentun Press, New York 1973, Chapters 3 and 4, respectively, and T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2^(nd) ed., John Wiley and Sons, New York, 1991, Chapters 2 and 3, whose disclosures are also incorporated by reference.

The substituent term “C₁-C₄ alkylthio” refers to sulfide groups such as methylthio, ethylthio, n-propylthio, isopropylthio, α-butylthio, t-butylthio and like groups.

The substituent term “C₁-C₄ alkylsulfoxide” indicates sulfoxide groups such as methylsulfoxide, ethylsulfoxide, α-propylsulfoxide, iso-propyl-sulfoxide, n-butylsulfoxide, sec-butylsulfoxide, and the like.

The term “C₁-C₄ alkylsulfonyl” encompasses groups such as methylsulfonyl, ethylsulfonyl, n-propylsulfonyl, isopropylsulfonyl, α-butylsulfonyl, t-butylsulfonyl, and the like.

Phenylthio, phenyl sulfoxide, and phenylsulfonyl compounds are known in the art and these have their art-recognized definitions. By “substituted phenylthio”, “substituted phenyl sulfoxide”, and “substituted phenylsulfonyl” is meant that the phenyl can be substituted as described above in relation to “substituted phenyl.”

The substituent terms “cyclic C₂-C₁₀ alkylene”, “substituted cyclic C₂-C₁₀ alkylene”, “cyclic C₂-C₁₀ heteroalkylene.” and “substituted cyclic C₂-C₁₀ heteroakylene” defines a cyclic group bonded (“fused”) to the phenyl radical. The cyclic group can be saturated or contain one or two double bonds. Furthermore, the cyclic group can have one or two methylene groups replaced by one or two oxygen, nitrogen or sulfur atoms.

The cyclic alkylene or heteroalkylene group can be substituted once or twice by substituents selected from the group consisting of hydroxy, protected-hydroxy, carboxy, protected-carboxy, keto, ketal, C₁-C₄ alkoxycarbonyl, C₁-C₄ alkanoyl, C₁-C₁₀ alkyl, carbamoyl, C₁-C₄ alkoxy, C₁-C₄, alkylthio, C₁-C₄ alkylsulfoxide, C₁-C₄ alkylsulfonyl, halo, amino, protected-amino, hydroxymethyl and a protected-hydroxymethyl group.

A cyclic alkylene or heteroalkylene group fused onto the benzene radical can contain two to ten ring members, but it preferably contains four to six members. Examples of such saturated cyclic groups include a bicyclic ring system that is a 2,3-dihydroindanyl or a tetralin ring. When the cyclic groups are unsaturated, examples occur when the resultant bicyclic ring system is a naphthyl ring or indanyl.

An example of a cyclic group that can be fused to a phenyl radical that has two oxygen atoms and that is fully saturated is dioxanyl. Examples of fused cyclic groups that each contain one oxygen atom and one or two double bonds occur when the phenyl ring is fused to a furyl, pyranyl, dihydrofuryl or dihydropyranyl ring. Cyclic groups that each have one nitrogen atom and contain one or two double more double bonds are illustrated where the phenyl is fused to a pyridino or pyrano ring. An example of a fused ring system having one nitrogen and two phenyl radicals is a carbozyl group. Examples of cyclic groups that each have one sulfur atom and contain one or two double bonds occur where the benzene ring is fused to a thieno, thiopyrano, dihydrothieno, or dihydrothiopyrano ring. Examples of cyclic groups that contain two heteroatoms selected from sulfur and nitrogen and one or two double bonds occur where the phenyl ring is fused to a thiazolo, isothiazolo, dihydrothiazolo or dihydroisothiazolo ring. Examples of cyclic groups that contain two heteroatoms selected from oxygen and nitrogen and one or two double bonds occur where the benzene ring is fused to an oxazole, isoxazole, dihydroxazole or dihydroisoxazole ring. Examples of cyclic groups that contain two nitrogen heteroatoms and one or two double bonds occur where the benzene ring is fused to a pyrazolo, imidazolo, dihydropyrazolo or dihydroimidazolo ring.

Examples of cyclic groups that each have one nitrogen atom and contain one or two double more double bonds occur when the phenyl is fused to a pyridino or pyrano ring. An example of a fused ring system having one nitrogen and two phenyl radicals is a carbozyl group. Examples of cyclic groups that each have one sulfur atom and contain one or two double bonds occur when the phenyl is fused to a thieno, thiopyrano, dihydrothieno, or dihydrothiopyrano ring.

Examples of cyclic groups that contain two heteroatoms selected from sulfur and nitrogen and one or two double bonds occur when the phenyl ring is fused to a thiazolo, isothiazolo, dihydrothiazolo or dihydroisothiazolo ring. Examples of cyclic groups that contain two heteroatoms selected from oxygen and nitrogen and one or two double bonds occur when the benzene ring, is fused to an oxazolo, isoxazolo, dihydroox-azolo or dihydroisoxazolo ring. Examples of cyclic groups which contain two nitrogen heteroatoms and one or two double bonds occur when the benzene ring is fused to a pyrazolo, Imidazolo, dihydropyrazolo or dihydroimidazolo ring.

Pharmaceutical Compositions

A pharmaceutical composition for treating infections, pain, or other indications treatable by a contemplated imidazo-imidazol-one is administered to a subject in need of the medication at dosage levels of about 0.7 to about 7000 mg per day, and preferably about 1 to about 500 mg per day, for a normal human adult of approximately 70 kg of body weight. This broadly translates into a dosage of about 0.01 to about 100 mg/kg of body weight per day of an imidizoimidazol-one compound of Formula I as active ingredient. The specific dosages employed, however, can be varied depending upon the requirements of the patient, the severity of the condition being treated, and the activity of the compound being employed. The determination of optimum dosages for a particular situation is within the skill of the art.

One or more of the imidizo-imidazol-one compounds of Formula I can be present as a pharmaceutically-acceptable salt. The term “pharmaceutically-acceptable salt” encompasses those salts that form with the carboxylate anions or ammonium cations and include salts formed with the organic and inorganic cations and anions discussed below. Furthermore, the term includes salts that form by standard acid-base reactions with basic groups (such as amino groups) and organic or inorganic acids. Such acids include hydrochloric, sulfuric, phosphoric, acetic, succinic, citric lactic, maleic, fumaric, palmitic, cholic, pamoic, mucic, D-glutamic, d-camphoric, glutaric, phthalic, tartaric, lauricc, stearic, salicyclic, methanesulfonic, benzenesulfonic, sorbic, picric, benzoic, cinnamic, and like acids.

The term “organic or inorganic cation” refers to counterions for the carboxylate anion of a carboxylate salt. The counter-ions are chosen from the alkali and alkaline earth metals, (such as lithium, sodium, potassium, barium and calcium): ammonium; and the organic cations such as (dibenzylammonium, benzylammonium, 2-hydroxymethylammonium, bis(2-hydroxyethyl)ammonium, phenylethylbenzyl ammonium, dibebenzylethylenediammoniurn, and like cations). Other cations encompassed by the above term include the protonated form of procaine, quinine and N-methylglucosamine, and the protonated forms of basic amino acids such as glycine, ornithine, histidine, phenylglycine, lysine and arginine. Furthermore, any zwitterionic form of the instant compounds formed by a carboxylic acid and an amino group is referred to by this term. A preferred cation for the carboxylate anion is the sodium cation.

A compound of Formula I can also be present as a solvate and hydrate. Thus, these compounds can crystallize with, for example, waters of hydration, or one, a number of, or any fraction thereof of molecules of the mother liquor solvent. The solvates and hydrates of such compounds are included within the scope of this invention.

One or more of the contemplated compounds can be in the biologically active ester form, such as the non-toxic, metabolically-labile ester-form. Such ester forms induce increased blood levels and prolong the efficacy of the corresponding non-esterified forms of the compounds. Ester groups that can be used include the lower alkoxymethyl groups (C₁-C₄ alkoxymethyl) for example, methoxymethyl, ethoxymethyl, isopropoxymethyl and the like; the -(C₁-C₄) alkoxyethyl groups, for example methoxyethyl, ethoxyethyl, propxyethyl, iso-propoxyethyl, and the like, the 2-oxo-1,3-dioxolen-4-ylmethyl groups such as 5-methyl-2-oxo-1,3-dioxolen-4-ylmethyl, 5-phenyl-2-oxo-1,3-dioxolen-4-ylmethyl, and the like, the C₁-C₃ alkylthiomethyl groups, for example methylthiomethyl, ethylthiomethyl, isopropylthiomethyl, and the like, the acyloxymethyl groups, for example pivaloyloxymethyl, pivaloyloxyethyl, α-acetoxymethyl, and the like, the ethoxycarbonyl-1-methyl group, the α-acetoxyethyl, the 3-phthalidyl or 5,6-dimethylphtalidyl groups, the 1-(C₁-C₄ alkyloxycarbonyloxy)-ethyl groups such as the 1-(ethoxycarbonyloxy)ethyl group, and the 1-(C₁-C₄ alkylaminocarbonyloxy)ethyl groups such as the 1-methylaminocarbonyloxyethyl group.

For preparing pharmaceutical compositions containing compounds of the invention, inert, pharmaceutically acceptable carriers are used. The pharmaceutical carrier can be either solid or liquid. Solid form preparations include, for example, powders, tablets, dispersible granules, capsules, cachets, and suppositories.

A solid carrier can be one or more substances that can also act as diluents, flavoring agents, solubilizers, lubricants, suspending agents, binders, or tablet disintegrating agents; it can also be an encapsulating material.

In powders, the carrier is generally a finely divided solid that is in a mixture with the finely divided active component. In tablets, the active compound is mixed with the carrier having the necessary binding properties in suitable proportions and compacted in the shape and size desired.

For preparing pharmaceutical composition in the form of suppositories, a low-melting wax such as a mixture of fatty acid glycerides and cocoa butter is first melted and the active ingredient is dispersed therein by, for example, stirring. The molten homogeneous mixture is then poured into convenient-sized molds and allowed to cool and solidify.

Powders and tablets preferably contain between about 5% to about 70% by weight of the active ingredient. Suitable carriers include, for example, magnesium carbonate, magnesium stearate, talc, lactose, sugar, pectin, dextrin, starch, tragacanth, methyl cellulose, sodium carboxymethyl cellulose, a low-melting wax, cocoa butter and the like.

A pharmaceutical composition can include the formulation of the active compound with encapsulating material as a carrier providing a capsule in which the active component (with or without other carriers) is surrounded by a carrier, which is thus in association with it. In a similar manner, cachets are also included.

Tablets, powders, cachets, and capsules can be used as solid dosage forms suitable for oral administration.

Liquid pharmaceutical compositions include, for example, solutions suitable for oral or parenteral administration, or suspensions, and emulsions suitable for oral administration. Sterile water solutions of the active component or sterile solutions of the active component in solvents comprising water, ethanol, or propylene glycol are examples of liquid compositions suitable for parenteral administration.

Sterile solutions can be prepared by dissolving the active component in the desired solvent system, and then passing the resulting solution through a membrane filter to sterilize it or, alternatively, by dissolving the sterile compound in a previously sterilized solvent under sterile conditions.

Aqueous solutions for oral administration can be prepared by dissolving the active compound in water and adding suitable flavorants, coloring agents, stabilizers, and thickening agents as desired. Aqueous suspensions for oral use can be made by dispersing the finely divided active component in water together with a viscous material such as natural or synthetic gums, resins, methyl cellulose, sodium carboxymethyl cellulose, and other suspending agents known to the pharmaceutical formulation art.

Preferably, the pharmaceutical composition is in unit dosage form. In such form, the composition is divided into unit doses containing appropriate quantities of the active urea. The unit dosage form can be a packaged preparation, the package containing discrete quantities of the preparation, for example, packeted tablets, capsules, and powders in vials or ampules. The unit dosage form can also be a capsule, cachet, or tablet itself, or it can be the appropriate number of any of these packaged forms.

Library Synthesis and Use

As used herein, a chemical or combinatorial “library” is an intentionally created collection of a plurality of structurally similar, but different molecules. By “structurally similar”, it is meant that the constituent compounds of a library have the same ring structure; i.e., a bicyclic imidizo-imidazol-one ring, and at least two positions at which substituents are bonded to the ring structure. It is preferred that the member compounds of the library also have the same substitution pattern of substituent groups; i.e., that the at least two substituents be bonded to the same ring positions in each member compound. The molecule members of the library are different in that each member has at least one different substituent group from the other members of the library. A library can contain two to thousands or millions of member compounds.

A particular library can also be comprised of members whose substituent groups are all different from each other. Thus, where the shared ring structure contains substituent groups at a plurality of positions, a library can be prepared in which the member molecules contain different groups at each position.

Alternatively, a plurality of sub-libraries or sets can also be prepared in which a first set has a first substituent that is held constant for all of the members (is present in all members) of the set, whereas the groups at the other substituent positions are different and constitute a mixture of groups at each substituent position. A second set of that plurality has a second, different, first substituent, and the same mixture of different groups at the other substituent positions. A third set of that plurality has a third, different first substituent, and the same mixture of different groups at the other substituent positions, and so on until one decides to stop making sets with different first substituents. Such set pluralities of structurally similar, but different compounds are also often referred to as libraries of libraries, and are particularly useful in ascertaining which compound or compounds of a library are active in an assay of choice.

A library can be prepared by the synthetic means discussed below or otherwise herein and screened for biological activity in a variety of formats (e.g. libraries of soluble molecules). Libraries of compounds can be attached to resin beads, silica chips or other solid supports). The libraries can be screened in any variety of assays, such as those detailed below as well as others useful for assessing the biological activity of imidazo-imidazol-ones. The libraries typically contain at least one active compound and are generally prepared such that the compounds are in equimolar quantities.

The nonsupport-bound library mixtures prepared herein were screened in solution in radio-receptor inhibition assays described in detail hereinafter. Deconvolution of highly active mixtures can then be carried out by iterative, or positional scanning methods. These techniques, the iterative approach or the positional scanning approach, can be utilized for finding ,other active compounds within the libraries of the present invention using any one of the below-described assays or others well known in the art.

The iterative approach is well-known and is set forth in general in Houghten et al., Nature, 354, 84-86 (1991) and Dooley et al., Science, 266, 2019-2022 (1994), both of which are incorporated herein by reference. In the iterative approach, for example, sub-libraries of a molecule having three variable groups are made wherein the first variable substituent is defined (known and held constant) within the sub-library. Each of the compounds with the defined variable group is reacted separately with each of the other possibilities at the second variable group position and the third variable position is a mixture of all of the possible substituents to form a plurality of sub-libraries whose first two substituent groups are known. These sub-libraries are each assayed to define the identity of the second variable in the sub-library having the highest activity in the screen of choice.

A new sub-library with the first two variable positions defined is separately reacted with each of the other possibilities at the remaining undefined variable position. As before, the identity of the third variable position in the sub-library having the highest activity is determined.

If more variables exist, this process is repeated for all variables, yielding the compound with each variable contributing to the highest desired activity in the screening process. Promising compounds from this process can then be synthesized on larger scale in traditional single-compound synthetic methods for further biological investigation.

The positional-scanning approach has been described for various libraries as described, for example, in R. Houghten et al. PCT/US91/08694 and U.S. Pat. No. 5,556,762, both of which are incorporated herein by reference. The positional scanning approach is used as described below in the preparation and screening of the libraries.

In the positional scanning approach, sub-libraries are made defining only one variable substituent with each set of sub-libraries and all possible sub-libraries with each single variable substituent defined (and all other possibilities at all of the other variable positions) is made and tested. From the instant description one skilled in the art can synthesize libraries wherein two fixed substituent positions are defined at a time. From the assaying of each single-variable defined library, the optimum substituent at that position is determined, pointing to the optimum or at least a series of compounds having a maximum of the desired biological activity. Thus, the number of sub-libraries for compounds with a single substituent position defined is the number of different substituents desired at that position, and the number of all the compounds in each sub-library is the product of the number of substituents at each of the other variables.

The [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one libraries and compounds of Formula I can be prepared according to the general reaction Scheme 1, which for ease of description is shown using single amino acids. The reaction scheme shown forms a single compound or enantiomeric pair of compounds of Formula I. Where libraries are desired, a mixture of amino acids (Boc-R¹aa-OH or Boc-R²aa-OH), or carboxylic acids (R³-CO₂H) is used for at least one of the coupling steps.

The individual compounds and libraries are prepared using solid-phase techniques. The solid-phase resin, here, p-methylbenzhydrylamine resin (p-MBHA), is indicated in Scheme 1 by the large circle and dash.

Starting from p-methylbenzhydrylamine (MBHA) resin-bound N-tert-butyloxycarbonyl (Boc) amino acid 1 (Boc-R¹aa-OH), the Boc group was removed using a mixture of trifluoroacetic acid (TFA) and dichloromethane (DCM). The resulting amine salt was neutralized, and the resulting primary amine was N-acylated with a second Boc-protected amino acid (Boc-R²aa-OH) as before, to provide the resin bound-monopeptide 2.

Following removal of the Boc protecting group using 55% of trifluoroacetic acid in dichloromethane, the resulting free amine was acylated with a carboxylic acid 3 (R³-CO₂H) in dimethylformamide (DMF) using diisopropylcarbodiimide (DICI) and hydroxybenzotriazole (HOBt) to effect coupling. The bicyclic [3,5,7]-1H-imidazo[1,5-a]-imidazol-2(3H)-one 4 was obtained via cyclization using the conditions of Bischler-Napieralski, with 25-fold excess of phosphorus oxychloride (POCl₃) in refluxing 1,4-dioxane in the presence of a 30-fold excess of anion exchange resin (AG® 3-X4) [Bischler, A.; Napieralski, B. Chem. Ber., (1893), 26, 1903; W. M. Whaley, T. R. Govindachari, Org. React., 6, 74 (1951); T. Kametani et al., Tetrahedron, 27, 5367 (1971); G. Fodor et al., Angew. Chem. Int. Ed., 11, 919 (1972); G. Fodor, S. Nagubandi, Tetrahedron, 36, 1279 (1980); idem, Heterocycles, 15, 165 (1981)]. More recent syntheses using freshly distilled POCl₃ in the absence of the anion exchange resin have provided yields in the range of about 80 percent. The desired products were readily obtained following cleavage from the resin with anhydrous HF in anisole to provide compound 4.

Following the strategy described in Scheme 1, with the parallel synthesis approach, commonly referred to as the “tea-bag” method [Houghten et al., Nature, 354: 84-86 (1991)], libraries are synthesized with 33 different amino acids to provide the R group at R¹, 33 different amino acids to provide the R group at R², and 92 different carboxylic acids to provide the R group at R³, in which the individual building blocks were varied, while fixing the remaining two positions.

Any variety of amino acids can be used with the present invention as described above to prepare a vast array of bicyclic [3,5,7]-1H-imidazo[1,5-a]-imidazol-2(3H)-one with different R¹, R² and R³ groups. As described above, thirty-three first amino acids were coupled to the resin, which amino acids provide the R¹ substituent group. The thirty-three amino acids included Ala, Phe, Gly, His(DNP), Ile, Lys(CBZ), Leu, Met, Arg(Tos), Nva, Ser(Bzl), Thr(Bzl), Val, Tyr(CHO), Tyr(BrZ), Nle, Cha, ala, phe, his(DNP), ile, lys(CBZ), leu, met, arg(Tos), ser(Bzl), thr(Bzl), val, trp(CHO), tyr(BrZ), nle, nva, cha.

After the above-described 33 reactions and removal of the BOC protecting group, a single amino acid (valine) was coupled as the second amino acid, thereby providing the R² group. After removal of the second BOC group, a single carboxylic acid, acetic acid, was coupled to provide the R³ group for the 33 different compounds. Those compounds were thereafter cyclized to form compounds of Formula I and cleaved from the resin.

Another set or sub-library of 33 compounds was prepared by reacting a single amino acid (valine) with the resin to provide one R¹ group. After removal of the BOC protecting group, each of the above 33 amino acids was then separately coupled to provide 33 resin-linked peptides with the same R¹ group and one of the 33 different R² groups. On removing the second BOC group, a single carboxylic acid (acetic acid) was bonded to the free amino group to provide a single R³ group for the resin-linked peptides. Theses compounds were also cyclized to form compounds of Formula I, and cleaved from the resin.

In a third set or sub-library preparation, a single amino acid (valine) was coupled to the resin to provide a single R¹ group, the BOC group was removed and a second amino acid (valine) was coupled to provide a single R² group and form a dipeptide. After removal of the second BOC group, the dipeptide was separately reacted with each of the 92 carboxylic acids listed in Table 2, below, to provide 92 different R³ groups. The acylated peptides were thereafter cyclized, cleaved from the solid support resin and recovered. Assays using those compounds are discussed hereinafter.

As used herein, abbreviations for the various amino acid side-chain protecting groups are as follows: “Trt” for trityl, “tBu” for tert-butyl, “Boc” or “BOC” for tert-butoxycarbonyl, “Tos” for toluenesulfonyl or tosyl, “DNP” for dinitrophenyl, “Bzl” for benzyl, “CHO” for formyl, “Brz” for 2-bromobenzyloxycarbonyl and “CBZ” for carbobenzoxy. As can be seen from the side chains exemplified in the table below, it should be appreciated from the above-described embodiments of R¹ and R² are merely illustrative of the R groups that can be present. Following usual notation, L-amino acids are referred to with an initial capital letter as in Val, whereas D-amino acids are referred to with an initial lower case letter as in ala.

TABLE 1 Amino acid name Side chain R Full 3-letter code (For R¹ and R²) Glycine Gly

Alanine Ala

Valine Val

Leucine Leu

Isoleucine Ile

Lysine Lys

Serine Ser

Threonine Thr

Phenylalanine Phe

Tyrosine Tyr

Norvaline Nva

Norleucine Nle

Naphthylalanine Nal

Cyclohexylalanine Cha

Methionine Met

Phenylglycine Phg

A variety of carboxylic acids can also be used in the acylation step of the reaction of Scheme 1, thereby providing a wide array of substituents at the R³ position of the bicyclic [3,5,7]-1H-imidazo[1,5 -a]imidazol-2(3H)-one. Ninety-two carboxylic acids were used in preparing the [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one libraries. The ninety-two R³ groups were provided by the following carboxylic acids:

TABLE 2 Exemplary Carboxylic Acids 1-Phenyl-1-Cyclopropanecarboxylic Acid 2-Phenylbutyric Acid 3-Phenylbutyric Acid m-Tolylacetic Acid 3-Fluorophenylacetic Acid 3-Bromophenylacetic Acid ααα-Trifluoro-m-tolyl-acetic Acid p-Tolylacetic Acid 4-Fluorophenylacetic Acid 3-Methoxyphenylacetic Acid 4-Bromophenylacetic Acid 4-Methoxyphenylacetic Acid 4-Ethoxyphenylacetic Acid 4-Isobutyl-α-methylphenylacetic Acid 3,4-Dichlorophenylacetic Acid 3,5-Bis(trifluoromethyl)phenylacetic Acid 3-(3,4-Dimethoxyphenyl)propionic Acid 4-Biphenylacetic Acid αMethylcinnamic Acid 2-(Trifluoromethyl)cinnamic Acid (3,4-Dimethoxyphenyl)acetic Acid 3,4-(Methylenedioxy)phenylacetic Acid 2-Methoxycinnamic Acid 3,4-(Methylenedioxy)cinnamic Acid 2-Hydroxycinnamic Acid Benzoic Acid 4-Chlorocinnamic Acid m-Anisic Acid 4-Isopropylbenzoic Acid 4-Vinylbenzoic Acid 4-Fluorobenzoic Acid 4-Bromobenzoic Acid 3,4-Dimethoxycinnamic Acid 4-Hydroxybenzoic Acid trans-Cinnamic Acid 3,4-Dimethylbenzoic Acid 3-Fluoro-4-methylbenzoic Acid 3-Bromo-4-methylbenzoic Acid 3-Iodo-4-methylbenzoic Acid 3,4-Dichlorobenzoic Acid 4-Biphenylcarboxylic Acid 3,4-Difluorobenzoic Acid m-Toluic Acid Phenylacetic Acid Hydrocinnamic Acid 3-Methoxy-4-methylbenzoic Acid 4-Phenylbutyric Acid 4-Butylbenzoic Acid 3,5-Dimethylbenzoic Acid 3,5-Bis(Trifluoromethyl)benzoic Acid 3,4-Dimethoxybenzoic Acid 4-Ethyl-4-biphenylcarboxylic Acid 3,4,5-Trimethoxybenzoic Acid 3,4,5-Triethoxybenzoic Acid Butyric Acid Heptanoic Acid Isobutyric Acid (+/−)-2-Methylbutyric Acid Isovaleric Acid 3-Methylvaleric Acid 4-Methylvaleric Acid (+/−)-2-Ethylhexanoic Acid Crotonic Acid Vinylacetic Acid trans-3-Hexenoic Acid 2-Ethyl-2-Hexenoic Acid p-Toluic Acid p-Anisic Acid Trimethylacetic Acid tert-Butylacetic Acid Cyclohexanecarboxylic Acid Cyclohexylacetic Acid Dicyclohexylacetic Acid Cyclohexanebutyric Acid Cycloheptanecarboxylic Acid Acetic Acid 2-Methylcyclopropanecarboxylic Acid Cyclobutanecarboxylic Acid Cyclopentanecarboxylic Acid 3-Cyclopentylpropionic Acid 2-Furoic Acid Cyclohexanepropionic Acid 4-Methyl-1-Cyclohexanecarboxylic Acid 4-tert-Butyl-Cyclohexanecarboxylic Acid 1-Adamantanecarboxylic Acid 4-Methylcyclohexaneacetic Acid 2,4-Hexadienoic Acid Tiglic Acid 2-Norbornaneacetic Acid 1-Adamantaneacetic Acid 2-Ethylbutyric Acid 2-Thiophenecarboxylic Acid

EXAMPLE 1 Individual Syntheses of [3,5,7]-1H-Imidazo[1,5-a]-imidazol-2(3H)-ones

The compounds listed below were prepared following the synthetic route illustrated and discussed in regard to Scheme 1, above. A total of 158 individual compound syntheses or pools were carried out, with 73 of those reactions yielding either no product, starting material or other than the expected product. The reason for the apparent failures is not completely understood, but is believed to be due to steric hindrance. Recent syntheses with about twenty compounds indicated yields of product in each synthesis when freshly distilled POCl₃ was used in the synthesis. The reagent used for the preparation of each of the three “R” groups; i.e., the amino acid or carboxylic acid, is listed in the three columns labeled R¹, R² and R³, respectively. Mass spectral data from the syntheses are shown in the right hand-most column of the table below.

I

Single R³ MW ] M + H major peak Pool # R¹ R² (Acid) (calc) (calc) (MW) found 1 Gly Val Acetic 179.11 180.11 2 Ala Val Acetic 193.12 194.12 194.1 3 Val Val Acetic 221.15 222.15 222.1 4 Leu Val Acetic 235.17 236.17 236.2 5 Ile Val Acetic 235.17 236.17 236.1 6 Ser Val Acetic 209.12 210.12 7 Thr Val Acetic 223.13 224.13 8 Lys Val Acetic 250.16 251.16 9 Arg Val Acetic 278.19 279.19 279.6 10 Met Val Acetic 253.12 254.12 11 Nle Val Acetic 235.17 236.17 236.2 12 Nva Val Acetic 221.15 222.15 222.2 13 Cha Val Acetic 275.2 276.20 276.2 14 Phe Val Acetic 269.15 270.15 15 Tyr Val Acetic 285.15 286.15 16 Trp Val Acetic 387.16 388.16 17 His(DNP) Val Acetic 425.14 426.14 426.2 18 ala Val Acetic 193.12 194.12 194.1 19 val Val Acetic 221.15 222.15 222.2 20 leu Val Acetic 235.17 236.17 236.2 21 ile Val Acetic 235.17 236.17 236.2 22 ser Val Acetic 209.12 210.12 23 thr Val Acetic 223.13 224.13 24 lys Val Acetic 250.16 251.16 25 arg Val Acetic 264.17 265.17 26 met Val Acetic 253.12 254.12 27 nle Val Acetic 235.17 236.17 236.2 28 nva Val Acetic 221.15 222.15 222.2 29 cha Val Acetic 275.2 276.20 276.2 30 phe Val Acetic 269.15 270.15 270.2 31 tyr Val Acetic 285.15 286.15 286.2 32 trp Val Acetic 308.16 309.16 33 his(DNP) Val Acetic 425.14 426.14 462 34 Val Gly Acetic 179.11 180.11 180.1 35 Val Ala Acetic 193.12 194.12 194.1 36 Val Val Acetic 221.15 222.15 222.1 37 Val Leu Acetic 235.17 236.17 236.1 38 Val Ile Acetic 235.17 236.17 236.1 39 Val Ser Acetic 209.12 210.12 40 Val Thr Acetic 223.13 224.13 41 Val Lys Acetic 250.16 251.16 251.2 42 Val Arg Acetic 278.19 279.19 279.2 43 Val Met Acetic 253.12 254.12 44 Val Nle Acetic 235.17 236.17 236.1 45 Val Nva Acetic 221.15 222.15 222.1 46 Val Cha Acetic 275.2 276.20 276.2 47 Val Phe Acetic 269.15 270.15 270.1 48 Val Tyr Acetic 285.15 286.15 286.1 49 Val Trp Acetic 387.16 388.16 50 Val His Acetic 425.14 426.14 426.2 51 Val Ala Acetic 193.12 194.12 194.1 52 Val Val Acetic 221.15 222.15 222.1 53 Val Leu Acetic 235.17 236.17 236.1 54 Val Ile Acetic 235.17 236.17 236.2 55 Val Ser Acetic 209.12 210.12 56 Val Thr Acetic 223.13 224.13 57 Val Lys Acetic 250.16 251.16 251.2 58 Val Arg Acetic 278.19 279.19 279.2 59 Val Met Acetic 253.12 254.12 254.1 60 Val nle Acetic 235.17 236.17 236.1 61 Val nva Acetic 221.15 222.15 222.1 62 Val cha Acetic 275.2 276.20 276.2 63 Val phe Acetic 269.15 270.15 270.1 64 Val tyr Acetic 285.15 286.15 286.1 65 Val trp Acetic 308.16 309.16 66 Val his Acetic 425.14 426.14 426.1 67 Val Val 1-Phenyl-1- 323.2 324.20 324.2 cyclopropane- carboxylic 68 Val Val 2-Phenyl-butyric 325.22 326.22 326.2 69 Val Val 3-Phenyl-butyric 325.22 326.22 326.2 70 Val Val m-Tolylacetic 311.2 312.20 312.2 71 Val Val 3-Fluoro- 315.17 316.17 316.2 phenylacetic 72 Val Val 3-Bromo- 375.11 376.11 376.2 phenylacetic 73 Val Val (α, α, α-Trifluoro- 365.17 366.17 366.2 m-Tolyl)acetic 74 Val Val p-Tolylacetic 311.2 312.20 312.2 75 Val Val 4-Fluoro- 315.17 316.17 316.1 phenylacetic 76 Val Val 3-Methoxy- 327.19 328.19 328.2 phenylacetic 77 Val Val 4-Bromo- 375.11 376.11 376.1 phenylacetic 78 Val Val 4-Methoxy- 327.19 328.19 328.2 phenylacetic 79 Val Val 4-Ethoxy- 341.21 342.21 342.2 phenylacetic 80 Val Val 4-Isobutyl- 367.26 368.26 368.1 alpha- methylphenyl- acetic 81 Val Val 3,4-Dichloro- 365.11 366.11 366.2 phenylacetic 82 Val Val 3,5-Bis- 433.16 434.16 434.1 (Trifluoro- methyl)- phenylacetic 83 Val Val 3-(3,4- 371.22 372.22 372.2 Dimethoxy- phenyl)- propionic 84 Val Val 4-Biphenyl- 373.22 374.22 374.2 acetic 85 Val Val α-Methyl- 323.2 324.20 324.2 cinnamic 86 Val Val 2-(Trifluoro- 377.17 378.17 378.2 methyl)cinnamic 87 Val Val (3,4-Dimethoxy- 357.21 358.21 358.2 phenyl)acetic 88 Val Val 3,4-(Methylene- 329.17 330.17 330.2 dioxy)phenyl- acetic 89 Val Val 2-Methoxy- 339.19 340.19 cinnamic 90 Val Val 3,4-(Methylene- 353.17 354.17 dioxy)cinnamic 91 Val Val 2-Hydroxy- 325.18 326.18 cinnamic 92 Val Val Benzoic 283.17 284.17 284.2 93 Val Val 4-Chloro- 343.15 344.15 344.2 cinnamic 94 Val Val m-Anisic 313.18 314.18 95 Val Val 4-Isopropyl- 325.22 326.22 326.2 benzoic 96 Val Val 4-Vinylbenzoic 309.18 310.18 97 Val Val 4-Fluoro-benzoic 301.16 302.16 302.2 98 Val Val 4-Bromo-benzoic 361.1 362.10 99 Val Val 3,4-Dimethoxy- 369.21 370.21 cinnamic 100 Val Val 4-Hydroxy- 299.16 300.16 benzoic 101 Val Val trans-Cinnamic 309.18 310.18 310.2 102 Val Val 3,4-Dimethyl- 311.2 312.20 312.2 benzoic 103 Val Val 3-Fluoro-4- 315.17 316.17 methylbenzoic 104 Val Val 3-Bromo-4- 375.11 376.11 376.1 methylbenzoic 105 Val Val 3-Iodo-4- 423.08 424.08 methylbenzoic 106 Val Val 3,4-Dichloro- 351.09 352.09 benzoic 107 Val Val 4-Biphenyl- 373.22 374.22 374.2 carboxylic 108 Val Val 3,4-Difluoro- 319.15 320.15 benzoic 109 Val Val m-Toluic 297.18 298.18 298.2 110 Val Val Phenylacetic 297.18 298.18 298.2 111 Val Val Hydrocinnamic 311.2 312.20 312.2 112 Val Val 3-Methoxy-4- 327.42 328.42 328.2 methylbenzoic 113 Val Val 4-Phenylbutyric 325.22 326.22 326.2 114 Val Val 4-Butylbenzoic 339.23 340.23 340.2 115 Val Val 3,5-Dimethyl- 311.2 312.20 312.2 benzoic 116 Val Val 3,5-Bis- 419.14 420.14 (Trifluoro- methyl) benzoic 117 Val Val 3,4-Dimethoxy- 343.19 344.19 benzoic 118 Val Val 4-Ethyl-4- 387.23 388.23 biphenyl- carboxylic 119 Val Val 3,4,5-Tri- 373.2 374.20 methoxybenzoic 120 Val Val 3,4,5-Tri- 415.25 416.25 416.2 ethoxy-benzoic 121 Val Val Butyric 249.18 250.18 250.2 122 Val Val Heptanoic 291.23 292.23 292.2 123 Val Val Isobutyric 249.18 250.18 250.2 124 Val Val (+/−)-2-Methyl- 263.2 264.20 264.2 butyric 125 Val Val Isovaleric 263.2 264.20 264.2 126 Val Val 3-Methylvaleric 277.22 278.22 278.2 127 Val Val 4-Methylvaleric 277.22 278.22 278.2 128 Val Val (+/−)-2-Ethyl- 305.25 306.25 306.2 hexanoic 129 Val Val Crotonic 247.17 248.17 130 Val Val Vinylacetic 247.17 248.17 248.2 131 Val Val trans-3-Hexenoic 275.2 276.20 276.3 132 Val Val 2-Ethyl-2- 303.23 304.23 304.2 hexenoic 133 Val Val p-Toluic 297.18 298.18 298.2 134 Val Val p-Anisic 313.18 314.18 314.2 135 Val Val Trimethylacetic 263.2 264.20 264.1 136 Val Val tert-Butylacetic 277.22 278.22 278.2 137 Val Val Cyclohexane- 289.22 290.22 290.2 carboxylic 138 Val Val Cyclohexyl- 303.23 304.23 304.3 acetic 139 Val Val Dicyclohexyl- 385.31 386.31 386.4 acetic 140 Val Val Cyclohexane- 331.26 332.26 332.3 butyric 141 Val Val Cycloheptane- 303.23 304.23 carboxylic 142 Val Val Acetic 221.15 222.15 222.2 143 Val Val 2-Methyl- 261.18 262.18 cyclopropane- carboxylic 144 Val Val Cyclobutane- 261.18 262.18 262.2 carboxylic 145 Val Val Cyclopentane- 275.2 276.20 276.2 carboxylic 146 Val Val 3-Cyclopentyl- 303.23 304.23 304.2 propionic 147 Val Val 2-Furoic 273.15 274.15 148 Val Val Cyclohexane- 317.25 318.25 318.3 propionic 149 Val Val 4-Methyl-1- 303.23 304.23 cyclohexane- carboxylic 150 Val Val 4-tert-Butyl- 345.28 346.28 cyclohexane- carboxylic 151 Val Val 1-Adamantane- 355.26 356.26 carboxylic 152 Val Val 4-Methylcyclo- 317.25 318.25 318.2 hexaneacetic 153 Val Val 2,4-Hexadienoic 273.18 274.18 154 Val Val Tiglic 261.18 262.18 155 Val Val 2-Norbornane- 315.23 316.23 316.2 acetic 156 Val Val 1-Adamantane- 355.26 356.26 356.3 acetic 157 Val Val 2-Ethylbutyric 277.22 278.22 278.2 158 Val Val 2-Thiophene- 351.09 352.09 carboxylic

NMR product data for individual compounds five syntheses carried out following the reaction route outlined above are provided below for compounds corresponding in structure to compound 4b of Scheme 1. Those compounds are referred to as compounds 4b¹⁻⁵.

Product data:

4b¹: ¹H NMR (500 MHz, CD₃OD) δ 6.85-7.27 (m, 10H), 5.25-5.35 (t, 1H), 3.75-3.85 (s, 2H), 3.4-3.6 (dd, 2H), 2.57 (s, 3H); HRMS (FAB) m/z 318.1590 found (M+H]⁺, 318.1606 calculated for C₂₀H₂₀N₃O⁺.

4b²: ¹H NMR (500 MHz, CD₃OD) δ 4.85-4.95 (m, 1H), 2.60 (s, 3H), 2.54-2.59 (m, 1H), 2.23 (s, 1H), 1.25-1.26 (d, 3H), 0.89-0.90 (d, 3H); HRMS (FAB) m/z 193.1214 found (M]⁺, 193.1215 calculated for C₁₀H₁₅N₃O.

4b³: ¹H NMR (500 MHz, CD₃OD) δ 7.15-7.41 (m, 5H), 4.8-5.0 (m, 2H), 3.97 (s, 2H) 2.59 (s, 3H), 1.27-1.28 (d, 3H), 0.90-0.92 (d, 3H); HRMS (FAB) m/z 269.1528 found (M]⁺, 269.1528 calculated for C₁₆H₁₉N₃O.

4b⁴: ¹H NMR (500 MHz, CD₃OD) δ 5.64 (s, 1H), 4.14 (s, 3H), 3.30 (s, 1H), 2.43 (s, 3H), 1.85-1.90 (dd, 6H); HRMS (FAB) m/z 193.1207 found (M]⁺, 193.1215 calculated for C₁₀H₁₅N₃O.

4b⁵: ¹H NMR (500 MHz, CD₃OD) δ 5.59-5.72 (m, 2H), 5.18-5.20 (d, 1H), 2.68-2.85 (m, 3H), 2.44 (d, 3H), 2.37 (s, 1H), 1.0-1.1 (dd, 6H). LCMS (ES) m/z 208.1 found [M+H]⁺, 208.14 calculated for C₁₁H₁₈N₃O⁺.

Compound R¹ R² R³ 4b¹ benzyl benzyl methyl 4b² 2-propyl methyl methyl 4b³ 2-propyl benzyl methyl 4b⁴ methyl 2-propyl methyl 4b⁵ benzyl benzyl 2-propyl

EXAMPLE 2 Binding Inhibition of the Rat Brain Mu Receptor by [3,5,7]-1H-Imidazo[1,5-a]-imidazol-2(3H)-one Compounds

The previously prepared [3,5,7]-1H-imidazo[1,5-a]-imidazol-2(3H)-one library of individual compounds was screened for the ability to inhibit the binding of [³H] [D-Ala²,MePhe⁴,Gly⁵-ol]enkephalin (DAMGO) that is known to bind specifically to the mu opiate receptor present in rat brain homogenates following literature procedures. [Dooley et al., Science, 266:2019(1994); U.S. Pat. No. 5,763,193.]

Preparation of rat brain membranes and the receptor binding assay were carried out as described in Dooley et al., Life Sci., 52:1509(1993). Each tube in the screening assay contained 0.08 mg of compound mixture per milliliter, 0.5 mL of membrane suspension (0.1 mg of protein), 7 nM ³H-labeled DAMGO [specific activity 36 Ci/mmol, obtained from the National Institute on Drug Abuse (NIDA) repository through Chiron Mimotopes PeptideSystems (San Diego, Calif.) and 50 mL of peptide mixture in 50 mM Tris-HCl buffer (pH 7.4). The final volume was 0.65 mL. The results of these screenings are shown in the table, below, wherein the “R” groups are as discussed for Example 1. The results are reported as percent inhibition of DAMGO binding.

[3,5,7]-1H-Imidazo[1,5-a]imidazol-2(3H)-one Compound Binding Inhibition of [³H]DAMGO

Pool Minus % % Inhi- # R¹ R² R³ Mean NSB* Bound bition 3 Val Val Acetic Acid 974.05 666.05 70 30 4 Leu Val Acetic Acid 980.1 672.10 70 30 5 Ileu Val Acetic Acid 1052.8 744.80 78 22 11 Nle Val Acetic Acid 756.05 448.05 47 53 12 Nva Val Acetic Acid 998.7 690.70 72 28 18 Ala Val Acetic Acid 989.15 681.15 71 29 19 Val Val Acetic Acid 1027.75 719.75 75 25 20 Leu Val Acetic Acid 787.6 479.60 50 50 21 Ileu Val Acetic Acid 833.5 525.50 55 45 27 Nle Val Acetic Acid 871.25 563.25 59 41 28 Nva Val Acetic Acid 932.9 624.90 66 34 29 Cha Val Acetic Acid 891.65 583.65 61 39 30 Phe Val Acetic Acid 929.9 621.90 65 35 34 Val Gly Acetic Acid 956.4 648.40 68 32 35 Val Ala Acetic Acid 753.5 445.50 47 53 36 Val Val Acetic Acid 940.6 632.60 66 34 37 Val Leu Acetic Acid 932.9 624.90 66 34 38 Val Ileu Acetic Acid 687.75 379.75 40 60 39 Val Ser Acetic Acid 41 Val Lys Acetic Acid 858.1 550.10 58 42 42 Val Arg Acetic Acid 581.65 273.65 29 71 44 Val Nle Acetic Acid 947.55 639.55 67 33 45 Val Nv Acetic Acid 902.55 594.55 62 38 46 Val Ch Acetic Acid 881.4 573.40 60 40 47 Val Ph Acetic Acid 897.8 589.80 62 38 48 Val Tyr Acetic Acid 728.5 420.50 44 56 51 Val Ala Acetic Acid 902.75 594.75 62 38 52 Val Val Acetic Acid 959.85 651.85 68 32 53 Val Leu Acetic Acid 988.95 680.95 71 29 54 Val Ileu Acetic Acid 815.2 507.20 53 47 59 Val Met Acetic Acid 874.75 566.75 59 41 60 Val Nle Acetic Acid 902.8 594.80 62 38 61 Val Nva Acetic Acid 677.65 369.65 39 61 62 Val Cha Acetic Acid 805 497.00 52 48 63 Val Phe Acetic Acid 854.35 546.35 57 43 64 Val Tyr Acetic Acid 710.9 402.90 42 58 67 Val Val 1-Phenyl-1-cyclo- 830 522.00 55 45 propanecarboxylic Acid 68 Val Val 2-Phenylbutyric 935.45 627.45 66 34 Acid 69 Val Val 3-Phenylbutyric 900.1 592.10 62 38 Acid 70 Val Val m-Tolylacetic 954.15 646.15 68 32 Acid 71 Val Val 3-Fluoro- 853.7 545.70 57 43 phenylacetic Acid 72 Val Val 3-Bromo- 563 255.00 27 73 phenylacetic Acid 73 Val Val (α, α, α, α-Trifluoro- 967.25 659.25 69 31 m-tolyl)acetic Acid 74 Val Val p-Tolylacetic 858.65 550.65 58 42 Acid 75 Val Val 4-Fluoro- 758.2 450.20 47 53 phenylacetic Acid 76 Val Val 3-Methoxy- 854 546.00 57 43 phenylacetic Acid 77 Val Val 4-Bromo- 682.95 374.95 39 61 phenylacetic Acid 78 Val Val 4-Methoxy- 775.2 467.20 49 51 phenylacetic Acid 79 Val Val 4-Ethoxy- 929.1 621.10 65 35 phenylacetic Acid 81 Val Val 3,4-Diclhloro- 988.3 680.30 71 29 phenylacetic Acid 82 Val Val 3,5-Bis- 911.65 603.65 63 37 (Trifluoromethyl)- phenylacetic Acid 84 Val Val 4-Biphenylacetic 850.4 542.40 57 43 Acid 87 Val Val (3,4-Dimethoxy- 870.35 562.35 59 41 phenyl)acetic Acid 88 Val Val 3,4- (Methylenedioxy)- cinnamic Acid 107 Val Val 4-Biphenyl- 804.2 496.20 52 48 carboxylic Acid 110 Val Val Phenylacetic Acid 818.7 510.70 54 46 113 Val Val 4-Phenylbutyric 716.3 408.30 43 57 Acid 121 Val Val Butyric Acid 826.45 518.45 54 46 122 Val Val Heptanoic Acid 817.3 509.30 53 47 123 Val Val Isobutyric Acid 832.5 524.50 55 45 124 Val Val (+/−)-2- 901.85 593.85 62 38 Methylbutyric Acid 125 Val Val Isovaleric Acid 763.7 455.70 48 52 126 Val Val 3-Methylvaleric 918.7 610.70 64 36 Acid 127 Val Val 4-Methylvaleric 909.6 601.60 63 37 Acid 128 Val Val (+/−)-2- 881.35 573.35 60 40 Ethylhexanoic Acid 135 Val Val Trimethylacetic 931.85 623.85 65 35 Acid 136 Val Val tert-Butylacetic 991 683.00 72 28 Acid 137 Val Val Cyclohexane- 933.35 625.35 66 34 carboxylic Acid 138 Val Val Cycloexylacetic 877.8 569.80 60 40 Acid 139 Val Val Dicyclo- 928.85 620.85 65 35 hexylacetic Acid 140 Val Val Cycloheptane- 615.55 307.55 32 68 carboxyic Acid 142 Val Val Acetic Acid 946.05 638.05 67 33 144 Val Val Cyclobutane- 867.3 559.30 59 41 carboxylic Acid 145 Val Val Cyclopentane- 986.9 678.90 71 29 carboxylic Acid 146 Val Val 3-Cyclopentyl- 945.85 637.85 67 33 propionic Acid 148 Val Val Cyclohexane- 890.8 582.80 61 39 propionic Acid 152 Val Val 4-Methyl-cyclo- 770.1 462.10 48 52 hexaneacetic Acid 155 Val Val 2-Norbornane- 918.35 610.35 64 36 acetic Acid 156 Val Val 1-Adamantane- 925.85 617.85 65 35 acetic Acid 157 Val Val 2-Thiophene- 930.35 622.35 65 35 carboxylic Acid *NSB = non-specific binding.

EXAMPLE 3 Binding Inhibition of the Guinea Pig Brain Kappa Receptor by [3,5,7]-1H-Imidazo[1,5-a]imidazol-2(3H)-one Compounds

The above-prepared library of individual compounds was screened for the ability to inhibit the binding of tritiated Compound U69,593 that is known to bind specifically to the kappa opiate receptor present in guinea pig brain homogenates following literature procedures. [Dooley et al., J. Biol. Chem., 273(30) 18848-18856 (1998)]

Briefly, guinea pig cortices and cerebella were homogenized in 40 mL of Buffer A [50 mM Tris-HCl, pH 7.4] at 4° C. Homogenates were centrifuged [Beckman® J2-HC, 35, 300×g] for 10 minutes. The pellets were resuspended in fresh buffer and incubated at 37° C. for 40 minutes. Following incubation, the suspensions were centrifuged as before, the resulting pellets resuspended in 100 volumes of Tris buffer, and the suspensions combined. Membrane suspensions were prepared and used on the same day. Protein content of the crude homogenates was determined by the method of Bradford, Anal. Biochem., 72:248-252 (1976).

Each assay tube contained 0.5 mL of membrane suspension, 3 nm of tritiated Compound U69,593 [(5a,7a,8b)-(−)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl)-benzeneacetamide; Lahti et al., European J. Pharmacol., 109:281-284(199-85)] in a total volume of 0.65 mL. Assay tubes were incubated for 2.5 hours a 25° C. The assay was then filtered through GF-B filters on a Tomec™ harvester (Orange, Conn.). The filters were subsequently washed with 6 mL of 50 mM Tris-HC₁, pH 7.4 at 4° C. Bound radioactivity was counted on a Wallace™ Beta-plate Liquid Scintillation Counter (Piscataway, N.J.). Unlabeled U50, 488 [(trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide) methane sulfonate hydrate; Lahti et al., Life Sci., 31:2257-xx(1982) and Von Voightlander et al., J. Pharmacol. Exp. Ther., 224:7 (1983)] was used as a competitive inhibitor to generate a standard curve and determine nonspecific binding. The results of these assays are shown in the table, below, wherein the “R” groups are as discussed for Example 1.

[3,5,7]-1H-Imidazo[1,5-a]imidazol-2(3H)-one Compound Binding Inhibition of [³H]U69,593

Pool Minus % % Inhi- # R¹ R² R³ Mean NSB Bound bition 3 Val Val Acetic Acid 1468.8 561.80 54.228 45.772 4 Leu Val Acetic Acid 1895.55 988.55 95.420 4.580 5 Ileu Val Acetic Acid 1684.45 777.45 75.043 24.957 11 Nle Val Acetic Acid 1736.15 829.15 80.034 19.966 12 Nva Val Acetic Acid 1680.95 773.95 74.706 25.294 18 Ala Val Acetic Acid 1818.85 911.85 88.016 11.984 19 Val Val Acetic Acid 1783.25 876.25 84.580 15.420 20 Leu Val Acetic Acid 1621.8 714.80 68.996 31.004 21 Ileu Val Acetic Acid 1496.7 589.70 56.921 43.079 27 Nle Val Acetic Acid 1734.3 827.30 79.855 20.145 28 Nva Val Acetic Acid 1607.35 700.35 67.601 32.399 29 Cha Val Acetic Acid 1821.55 914.55 88.277 11.723 30 Phe Val Acetic Acid 1682.8 775.80 74.884 25.116 34 Val Gly Acetic Acid 1726.65 819.65 79.117 20.883 35 Val Ala Acetic Acid 1711.9 804.90 77.693 22.307 36 Val Val Acetic Acid 1787.35 880.35 84.976 15.024 37 Val Leu Acetic Acid 1559.4 652.40 62.973 37.027 38 Val Ileu Acetic Acid 1618.1 711.10 68.639 31.361 39 Val Ser Acetic Acid 1723.65 816.65 78.827 21.173 41 Val Lys Acetic Acid 1444.2 537.20 51.853 48.147 42 Val Arg Acetic Acid 1406.35 499.35 48.200 51.800 44 Val Nle Acetic Acid 2049.7 1142.70 110.299 −10.299 45 Val Nv Acetic Acid 1790.45 883.45 85.275 14.725 46 Val Ch Acetic Acid 2169 1262.00 121.815 −21.815 47 Val Ph Acetic Acid 1989.3 1082.30 104.469 −4.469 48 Val Tyr Acetic Acid 1784 877.00 84.653 15.347 51 Val Ala Acetic Acid 1645.8 738.80 71.313 28.687 52 Val Val Acetic Acid 1681.35 774.35 74.744 25.256 53 Val Leu Acetic Acid 2008.85 1101.85 106.356 −6.356 54 Val Ileu Acetic Acid 1947.25 1040.25 100.410 −0.410 59 Val Met Acetic Acid 1724.95 817.95 78.953 21.047 60 Val Nle Acetic Acid 1755.4 848.40 81.892 18.108 61 Val Nva Acetic Acid 1433.75 526.75 50.845 49.155 62 Val Cha Acetic Acid 1776.3 869.30 83.909 16.091 63 Val Phe Acetic Acid 1786.7 879.70 84.913 15.087 64 Val Tyr Acetic Acid 1545.5 638.50 61.631 38.369 67 Val Val 1-Phenyl-1-cyclo 1784.1 877.10 84.662 15.338 propanecarboxylic Acid 68 Val Val 2-Phenylbutyric 2013.3 1106.30 106.786 −6.786 Acid 69 Val Val 3-Phenylbutyric 1602.75 695.75 67.157 32.843 Acid 70 Val Val m-Tolylacetic Acid 2019.55 1112.55 107.389 −7.389 71 Val Val 3-Fluoro- 1541.5 634.50 61.245 38.755 phenylacetic Acid 72 Val Val 3-Bromo- 1588.15 681.15 65.748 34.252 phenylacetic Acid 73 Val Val (α, α, α, α-Trifluoro- 1717.2 810.20 78.205 21.795 m-tolyl)acetic Acid 74 Val Val p-Tolylacetic Acid 1407.25 500.25 48.287 51.713 75 Val Val 4-Fluoro- 1643.95 736.95 71.134 28.866 phenylacetic Acid 76 Val Val 3-Methoxy- 1859.1 952.10 91.902 8.098 phenylacetic Acid 77 Val Val 4-Bromo- 1670.1 763.10 73.658 26.342 phenylacetic Acid 78 Val Val 4-Methoxy- 1812.05 905.05 87.360 12.640 phenylacetic Acid 79 Val Val 4-Ethoxy- 1842.9 935.90 90.338 9.662 phenylacetic Acid 81 Val Val 3,4-Diclhloro 1831.35 924.35 89.223 10.777 phenylacetic Acid 82 Val Val 3,5-Bis- 1638.3 731.30 70.589 29.411 (Trifluoromethyl)- Phenylacetic Acid 84 Val Val 4-Biphenylacetic 1628.3 721.30 69.624 30.376 Acid 87 Val Val (3,4- 1749.65 842.65 81.337 18.663 Dimethoxyphenyl)- acetic Acid 88 Val Val 3,4- 1739.6 832.60 80.367 19.633 (Methylenedioxy)- Cinnamic Acid 107 Val Val 4-Biphenyl- 2089.6 1182.60 114.151 −14.151 carboxylic Acid 110 Val Val Phenylacetic Acid 1667.95 760.95 73.451 26.549 113 Val Val 4-Phenylbutyric 1545.15 638.15 61.597 38.403 Acid 121 Val Val Butyric Acid 1533.45 626.45 60.468 39.532 122 Val Val Heptanoic Acid 1443.7 536.70 51.805 48.195 123 Val Val Isobutyric Acid 1498.8 591.80 57.124 42.876 124 Val Val (+/−)-2-Methyl- 1555.85 648.85 62.630 37.370 butyric Acid 125 Val Val Isovaleric Acid 1553.3 646.30 62.384 37.616 126 Val Val 3-Methylvaleric 1666.5 759.50 73.311 26.689 Acid 127 Val Val 4-Methylvaleric 1592.6 685.60 66.178 33.822 Acid 128 Val Val (+/−)-2-Ethyl- 1503.35 596.35 57.563 42.437 hexanoic Acid 135 Val Val Trimethylacetic 1623.6 716.60 69.170 30.830 Acid 136 Val Val tert-Butylacetic 1741.9 834.90 80.589 19.411 Acid 137 Val Val Cyclohexane- 2249.85 1342.85 129.619 −29.619 carboxylic Acid 138 Val Val Cycloexylacetic 1639.3 732.30 70.685 29.315 Acid 139 Val Val Dicyclohexyl- 1515.95 608.95 58.779 41.221 acetic Acid 140 Val Val Cycloheptane- 1424 517.00 49.903 50.097 carboxyic Acid 142 Val Val Acetic Acid 1728.8 821.80 79.324 20.676 144 Val Val Cyclobutane- 1447.5 540.50 52.172 47.828 carboxylic Acid 145 Val Val Cyclopentane- 1544.15 637.15 61.501 38.499 carboxylic Acid 146 Val Val 3-Cyclopentyl- 1622.75 715.75 69.088 30.912 propionic Acid 148 Val Val Cyclohexane- 1839.1 932.10 89.971 10.029 propionic Acid 152 Val Val 4-Methylcyclo- 1515.1 608.10 58.697 41.303 hexaneacetic Acid 155 Val Val 2-Norbornane- 1622.25 715.25 69.040 30.960 acetic Acid 156 Val Val 1-Adamantane- 1723.4 816.40 78.803 21.197 acetic Acid 157 Val Val 2-Thiophene- 1473.05 566.05 54.638 45.362 carboxylic Acid

EXAMPLE 4 Preparation of Libraries of [3,5,7]-1H-Imidazo[1,5-a]imidazol-2(3H)-one Compounds

Libraries of [3,5,7]-1H-imidazo[1,5-a]imidazol-2(3H)-one compounds are prepared analogously to the preparation of individual compounds discussed in Example 1. However, whereas a single reagent was used to provide each of the R groups of the intermediates prepared in the syntheses of the individual compounds of Example 1, both single reactants and mixtures of reactants are used to provide the R¹, R² and R³ groups for the different library pools of mixed compounds. As is discussed in treated detail below, 33 library pools are prepared in which R¹ is an individual amino acid side chain, with separate pools containing mixtures of 33 amino acids of different side chains (R²) and 92 different carboxylic acid chains (R³).

Where individual reactants are used to provide a particular R group, the procedures of Example 1 are followed. Where mixtures are desired at a particular R group, the protected amino acids or carboxylic acids are provided in mixtures. The mixtures used to provide the various R groups are listed in the table, below, with the relative molar amount of each reactant being listed.

TABLE 4 Mixtures of Reactants Used to Prepare [3,5,7]-1H-Imidazo[1,5-a]imidazol-2(3H)-one Mixed Compound Library R¹ R² R³ Boc-amino Boc-amino Carboxylic acid acids Reagent Ratio acids Reagent Ratio Reagent Ratio Boc-L-Ala 0.95 Boc-L-Ala 0.95 1-Phenyl-1- 1.00 cyclopropane- carboxylic Acid Boc-L-Phe 0.81 Boc-L-Phe 0.81 2-Phenylbutyric 1.20 Acid Boc-Gly 1.00 Boc-Gly 1.00 3-Phenylbutyric 2.60 Acid Boc-L- 0.85 Boc-L-His(DNP) 0.85 m-Tolylacetic Acid 1.80 His(DNP) Boc-L-Ile 1.16 Boc-L-Ile 1.16 3-Fluorophenyl- 0.84 acetic Acid Boc-L- 1.05 Boc-L-Lys(CBZ) 1.05 3-Bromophenyl- 0.61 Lys(CBZ) acetic Acid Boc-L-Leu 1.08 Boc-L-Leu 1.08 (α,α,α-Trifluoro-m- 0.61 Tolyl)acetic Acid Boc-L-Met 0.89 Boc-L-Met 0.89 p-Tolylacetic Acid 1.36 Boc-L- 1.42 Boc-L-Arg(Tos) 1.42 4-Fluorophenyl- 1.04 Arg(Tos) acetic Acid Boc-L- 1.30 Boc-L-Ser(Bzl) 1.30 3-Methoxyphenyl- 1.17 Ser(Bzl) acetic Acid Boc-L- 1.60 Boc-L-Thr(Bzl) 1.60 4-Bromophenyl- 0.88 Thr(Bzl) acetic Acid Boc-L-Val 1.14 Boc-L-Val 1.14 4-Methoxyphenyl- 1.80 acetic Acid Boc-L- 0.89 Boc-L-Trp(CHO) 0.89 4-Ethoxyphenyl- 1.40 Trp(CHO) acetic Acid Boc-L- 1.26 Boc-L-Tyr(Brz) 1.26 4-Isobutyl-a- 1.70 Tyr(Brz) methylphenylacetic Acid Boc-D-Ala 0.95 Boc-D-Ala 0.95 3,4-Dichloro- 0.81 phenylacetic Acid Boc-D-Phe 0.81 Boc-D-Phe 0.81 3,5-Bis- 0.50 (Trifluoromethyl)- phenylacetic Acid Boc-D- 0.85 Boc-D-His(DNP) 0.85 3-(3,4-Dimethoxy- 2.20 His(DNP) phenyl)propionic Acid Boc-D-Ile 1.16 Boc-D-Ile 1.16 4-Biphenylacetic 1.40 Acid Boc-D- 1.05 Boc-D-Lys(CBZ) 1.05 α-Methylcinnamic 1.95 Lys(CBZ) Acid Boc-D-Leu 1.08 Boc-D-Leu 1.08 2- 1.03 (Trifluoromethyl)- cinnamic Acid Boc-D-Met 0.89 Boc-D-Met 0.89 (3,4-Dimethoxy- 1.44 phenyl)acetic Acid Boc-D- 1.42 Boc-D-Arg(Tos) 1.42 3,4-(Methylene- 1.27 Arg(Tos) dioxy)phenylacetic Acid Boc-D- 1.30 Boc-D-Ser(Bzl) 1.30 2-Methoxycinnamic 5.60 Ser(Bzl) Acid Boc-D- 1.60 Boc-D-Thr(Bzl) 1.60 3,4-(Methylene- 10.40 Thr(Bzl) dioxy)cinnamic Acid Boc-D-Val 1.14 Boc-D-Val 1.14 2-Hydroxy-cinnamic 4.90 Acid Boc-D- 0.89 Boc-D-Trp(CHO) 0.89 Benzoic Acid 1.28 Trp (CHO) Boc-D- 1.26 Boc-D-Tyr(BrZ) 1.26 4-Chlorocinnamic 2.95 Tyr (BrZ) Acid Boc-L- 1.15 Boc-L- 1.15 m-Anisic Acid 1.52 Norvaline Norvaline Boc-D- 1.15 Boc-D- 1.15 4-Isopropyl- 3.00 Norvaline Norvaline benzoic Acid Boc-L- 1.15 Boc-L- 1.15 4-Vinylbenzoic 1.50 Norleucine Norleucine Acid Boc-D- 1.15 Boc-D- 1.15 4-Fluorobenzoic 1.22 Norleucine Norleucine Acid Boc-L- 1.50 Boc-L- 1.50 4-Bromobenzoic 0.59 Cyclohexyl- Cyclohexyl- Acid alanine alanine Boc-D- 1.50 Boc-D- 1.50 3,4-Dimethoxy- 7.27 Cyclohexyl- Cyclohexyl- cinnamic Acid alanine alanine 4-Hydroxybenzoic 7.61 Acid trans-Cinnamic Acid 4.20 3,4-Dimethyl- 2.44 benzoic Acid 3-Fluoro-4-methyl- 0.75 benzoic Acid 3-Bromo-4-methyl- 0.86 benzoic Acid 3-Iodo-4-methyl- 0.84 benzoic Acid 3,4-Dichloro- 0.39 benzoic Acid 4-Biphenyl- 5.10 carboxylic Acid 3,4-Difluoro- 0.45 benzoic Acid m-Toluic Acid 1.60 Phenylacetic Acid 1.00 Hydrocinnamic Acid 2.50 3-Methoxy-4- 2.10 methylbenzoic Acid 4-Phenylbutyric 3.00 Acid 4-Butylbenzoic 2.60 Acid 3,5-Dimethyl- 1.94 benzoic Acid 3,5-Bis- 0.96 (Trifluoromethyl)- Benzoic Acid 3,4-Dimethoxy- 3.08 benzoic Acid 4-Ethyl-4- 0.92 biphenylcarboxylic Acid 3,4,5-Trimethoxy- 1.46 benzoic Acid 3,4,5-Triethoxy- 2.37 benzoic Acid Butyric Acid 3.39 Heptanoic Acid 3.51 Isobutyric Acid 3.11 (+/−)-2-Methyl- 6.25 butyric Acid Isovaleric Acid 6.36 3-Methylvaleric 5.06 Acid 4-Methylvaleric 3.32 Acid (+/−)-2-Ethyl- * hexanoic Acid Crotonic Acid 5.26 Vinylacetic Acid 1.30 trans-3-Hexenoic * Acid 2-Ethyl-2-hexenoic 11.63 Acid p-Toluic Acid 2.28 p-Anisic Acid 5.38 Trimethylacetic 4.24 Acid tert-Butylacetic * Acid Cyclohexane- 3.51 carboxylic Acid Cyclohexylacetic 3.95 Acid Dicyclohexylacetic * Acid Cyclohexanebutyric 3.33 Acid Cycloheptane- 2.60 carboxylic Acid Acetic Acid 2.65 2-Methylcyclo- 2.42 propanecarboxylic Acid Cyclobutane- 2.77 carboxylic Acid Cyclopentane- 3.03 carboxylic Acid 3-Cyclopentyl- 3.71 propionic Acid 2-Furoic Acid 4.44 Cyclohexane- 2.80 propionic Acid 4-Methyl-1-cyclo- 5.92 hexanecarboxylic Acid 4-tert-Butyl- 6.64 cyclohexane- carboxylic Acid 1-Adamantane- * carboxylic Acid 4-Methylcyclo- 4.79 hexaneacetic Acid 2,4-Hexadienoic * Acid Tiglic Acid 4.59 2-Norbornane- 5.45 acetic Acid 1-Adamantane- 11.16 acetic Acid 2-Ethylbutyric * Acid 2-Thiophene- 1.16 carboxylic Acid *ratio not determined

Each of the patents and articles cited herein is incorporated by reference. The use of the article “a” or “an” is intended to include one or more.

The foregoing description and the examples are intended as illustrative and are not to be taken as limiting. Still other variations within the spirit and scope of this invention are possible and will readily present themselves to those skilled in the art. 

What is claimed:
 1. A compound having a structure corresponding to that shown in Formula I, below, or a pharmaceutically acceptable salt thereof:

wherein: R¹ and R² are independently selected from the group consisting of a hydrido, methyl, benzyl, 2-butyl, aminobutyl, N,N-dimethylaminobutyl, N-methylaminobutyl, N-methyl-N-benzylaminobutyl, 2-methylpropyl, methylsulfinylethyl, methylthioethyl, N,N-dimethylaminoethyl, N,N-dimethylaminopropyl, N,N,N-trimethylguanidinopropyl, N,N,N-tribenzylguanidinopropyl, N,N-dibenzylguanidinopropyl, N-methylguanidinopropyl, hydroxymethyl, 1-hydroxyethyl, 2-propyl, N-methyl-3-indolylmethyl, 4-methoxybenzyl, 4-hydroxybenzyl, propyl, butyl, cyclohexylmethyl, phenyl, 2-naphthylmethyl, and a 4-imidazolylmethyl substituent; and R³ is selected from the group consisting of a hydrido, C₁-C₁₀ alkyl, C₁-C₁₀ substituted alkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ substituted alkenyl, C₂-C₁₀ alkynyl, C₂-C₁₀ substituted alkynyl, C₃-C₇ substituted cycloalkyl, phenyl, C₇-C₁₆ phenylalkyl, C₇-C₁₆ phenylalkenyl, C₇-C₁₆ phenylalkenyl and a C₇-C₁₆ substituted phenylalkenyl group.
 2. The compound according to claim 1 wherein R³ is selected from the group consisting of a 1-phenyl-1-cyclopropyl, 1-phenylbutyl, 2-phenylbutyl, 3-fluorobenzyl, 3-bromobenzyl, α,α,α-trifluoro-m-xylyl, p-xylyl, 4-fluorobenzyl, 3-methoxybenzyl, 4-bromobenzyl, 4-methoxybenzyl, 4-ethoxybenzyl, 4-isobutyl-α-methylbenzyl, 3,4-dichlorobenzyl, 3,5-bis-(trifluoromethyl)benzyl, 2-(3,4-dimethoxyphenyl)ethyl, 4-biphenylmethyl, β-methylstyryl, 2-(trifluoromethyl)-styryl, 3,4-dimethoxybenzyl, 3,4-dihydroxybenzyl, 2-methoxyatyryl, 3,4-dihydroxystyryl, 2-hydroxystyryl, pheryl, 4-chlorostyryl, 3-methoxyphenyl, 4-isopropylphenyl, 4-vinylphenyl, 4-fluorophenyl, 4-bromophenyl, 3,4-dimethoxystyryl, 4-hydroxyphenyl, trans-styryl, 3,4-dimethylphenyl, 3-fluoro-4-methylphenyl, 3-bromo-4-methyl-phenyl, 3-iodo-4-methyl-phenyl, 3,4-dichlorophenyl, 4-biphenyl, 3,4-difluorophenyl, m-tolyl, benzyl, phenethyl, 3-methoxy-4-methylphenyl, 3-phenylpropyl, 4-butylphenyl, 3,5-dimethylphenyl, 3,5-bis-(trifluoromethyl)phenyl, 3,4-dimethoxyphenyl, 4-ethyl-4-biphenyl, 3,4,5-triethoxyphenyl, propyl, hexyl, isopropyl, 2-butyl, isobutyl, 2-pentyl, isovaleryl, 3-heptyl, 1-propenyl, 2-propenyl, trans-2-pentenyl, 1-ethyl-1-pentenyl, p-tolyl, p-anisyl, t-butyl, neopentyl, cyclohexyl, cyclohexylmethyl, dicyclohexylmethyl, cyclohexylpropyl, cycloheptyl, methyl, 2-methyl cyclopropyl, cyclobutyl, cyclopentyl, cyclopentylethyl, 2-furyl, cyclohexylethyl, 4-methylcyclohexyl, 4-tert-butyl-cyclohexyl, 1-adamantyl, 4-methylcyclohexylmethyl, 1,3-pentadienyl, 2-buten-2-yl, 2-norbornanemethyl, 1-adamantanemethyl, 3-pentyl, and a 2-thiophene substituent.
 3. The compound according to claim 1 wherein the R¹ substituent is selected from the side chain of the α-carbon of an amino acid selected from the group consisting of Ala, Phe, Gly, His, Ile, Lys, Leu, Met, Arg, Nva, Ser, Thr, Val, Tyr, Tyr, Nle, Cha, ala, phe, his, ile, lys, leu, met, arg, ser, thr, val, trp, tyr, nle, nva, and cha, wherein amino acids written in all lower case letters are D-amino acids.
 4. The compound according to claim 1 wherein the R² substituent is selected from the side chain of the α-carbon of an amino acid selected from the group consisting of Ala, Phe, Gly, His, Ile, Lys, Leu, Met, Arg, Nva, Ser, Thr, Val, Tyr, Tyr, Nle, Cha, ala, phe, his, ile, lys, leu, met, arg, ser, thr, val, trp, tyr, nle, nva, and cha, wherein amino acids written in all lower case letters are D-amino acids.
 5. A compound having a structure corresponding to that shown in the formula below, or a pharmaceutically acceptable salt thereof:

wherein: R¹ and R² are independently benzyl, methyl or 2-propyl and R³ is methyl or 2-propyl.
 6. The compound according to claim 5 wherein R¹ and R² are benzyl and R³ is methyl.
 7. The compound according to claim 5 wherein R¹ is 2-propyl, and R² and R³ are methyl.
 8. The compound according to claim 5 wherein R¹ is 2-propyl, R² is benzyl and R³ is methyl.
 9. The compound according to claim 5 wherein R¹ is methyl, R² is 2-propyl and R³ is methyl.
 10. The compound according to claim 5 wherein R¹ and R² are benzyl and R³ is 2-propyl. 